January Meme. Kingdom Swap
I wll say something about the swap suggestion that inspired this question at the end, because I have my own opinion about it, unsurprisingly, but first, here are some spontanous 18th Century ideas from yours truly. I tried to pick contemporaries of the same generation:
Kingdom Swap 1: Friedrich Wilhelm I. (Prussia) swaps with his first cousin George II (Britain and Hannover)
This fulfills one of FW's dreams, if some of his sidekicks are to be believed. FW as King of Great Britain was an actual possibility for a hot minute, because the childless William of Orange (and III of England) considered adopting him. (They were doubly related.) (This would not have conflicted with the Act of Succession by Parliament settling the English crown on Sophia of Hannover (granddaughter of James I and VI) and her issue, because FW was Sophia's grandson as much as G2. But if William of Orange had adopted him, there would have been no George I (Sophie's son), let alone a G2 (and so forth); the Brits would have gotten a Hohenzollern instead of a Hannover dynasty. (Making G2 the King in Prussia, otoh, has no logical AU explanation, but never mind, we're in it for the crack and the fun.) In our timeline, FW and cousin G2 loathed each other ever since they were boys and FW, despite being a few years younger, managed to beat no longer future G2 up. This set the tone for their entire relationship, which included such highlights as George marrying FW's first crush, the two of them almost fighting a personal combat style duel as monarchs in 1729 and the interminable marriage negotiations between their two oldest kids which contributed to the disastrous escape attempt of future Frederick the Great.
How would it have worked out if they'd swapped kingdoms: welllllll. On the one hand, FW might have been an awful human being, but he was one of the hardest workers ever to sit on a throne. There's a reason why even today, you have some historians making the case that in terms of his "interior" politics (not sure that's the right word for Innenpolitik), he was the best King Prussia ever had, including his son (i.e. Frederick the Great). (This also says something about the not so great Prussian Kings that came later, and then the Emperors, good lord, the Emperors, of course.) He took over a newly declared kingdom and former duchy and barony in considerable financial distress, which consisted of a couple of territories with no shared border, and left it financially and economically sound, with a well filled treasury, lots of new schools and hospitals founded (and state-financed), not to mention that he was the monarch to make school attendance obligatory. And for all that he had a fetish for the military (to put it mildly), he actually was not repeat, not set on starting actual wars. (As a young man, he participated in one of the bloodiest battles in European history after the Thirty Years War and before WWI, the battle of Malplaquet, which was part of the War of the Spanish Succession. This is believed to be the cause of him not starting any wars of his own but only providing his perfectly drilled troops for the various pan-European Wars like the one of the Polish Succession where they fought as part of the HRE (to simplify it). And he wasn't a hypocrite with his austerity programs; he cut down all court expenses and shut down royal residences left by his opulence loving father and grandfather except for a very few. As FW had been the kind of prince who gets a nice bit of real estate and hunting lodge by his parents at age 10 and manages to make it self sufficient and exporting goods by the time he's grown up, freaking out his parents by the fact he's an enthusiastic bookkeeper, I think that trait of his would survive any transplant.
On the other hand: that temper. Good lord, that temper. I mean, the Hannover Georges weren't wonders of stoicism, either, and the father and son loathing through the generations would remain equal, but none of the Georges were throwing their teachers down the stairs before they reached puberty. I think FW would do badly with the whole (relatively new, post Glorious Revolution) constitutional monarch part. Convinced he knew best, he would: lecture the Archbishop of Canterbury on how to be a proper Protestant (none of that High Church Popery for FW!), tell Parliament he had a couple of laws envisioned they really needed to pass, and piss off the entire English nobility on every level in record time. As it was, the Brits were very snobbish indeed about the Hannover. (G1 wasn't a brilliant mind, but he had the avarage continental prince education, meaning he was fluent in French in addition to German, and could make conversation in Italian and Dutch, and had enough Latin to talk with some of his English ministers in it who of course could speak neither German nor French (properly) at the start. How does this show up in English memoirs? As complaints he didn't any languages. Meaning he didn't speak English.) And the Hannover cousins were trying to fit in, and bringing your avarage baroque and Rokoko expense willingness to the table. FW would have shut any royal residences in and around London safe for two (one for summer, one in town for winter), he would have expected the nobility to provide at least one son each for the army and otherwise to develop a work for the state mentality, he'd have ignored balls and sure as hell wouldn't have organized some, and while he actually liked Händel, his idea of enjoying Händel's compositions in rl was to let them be played by army musicians (to save money). He sure as hell wouldn't have sponsored any opera performances. As for the sciences, he'd have seen the sense in encouraging medical developments and anything that's useful for economics, farming, import/export, but more abstract mathematics? Art? Nah. Oh, and anyone male and tall from the Orkney islands to the southern most part of Cornwall, not to mention the Colonies, should be prepared to get kidnapped so he can serve in FW's personal regiment of Windsor Giants.
So, my guess is: after only a few years of FW, both Whigs and Tories get together to conspire with the Queen to use his next big fit of temper to declare him insane and have a Regency installed.
Meanwhile in Prussia: (No longer) G2 is an okay King for the era. No idea whether he manages to make Prussia solvent, let alone fill the treasury, but the Hannovers weren't doing badly, economy wise, while still being Princes Elector, pre Britain, so let's say he does, if not to the same extent, and far slower. He might actually go to war about Jülich/Berg (don't ask, it's an eternal claim and grudge thing for generations of German monarchs), though, since participating in the same War of the Spanish Succession FW did (also just in a single battle, though a different one) left him wanting more, not less. What he most certainly does not manage, though, is creating what people think of when they talk about "Prussian mentality". His wife, Caroline, as Queen is far more socially and culturally active than FW's wife Sophia Dorothea was, and since her marriage with George is very different from the FW/SD disaster, she gets the necessary budget to continue her mentor Sophia Charlotte's "Athens on the Spree" project. The Berlin Academy florishes. (The overall economy might not, or at least not to the same degree.) No longer G2 has the same awful relationship with his oldest son as he did in rl because that's how Hannovers (and Hohenzollern) roll, so we still might get a Prussian Crown Prince escape attempt (or successful escape?) around 1730. If no longer Fritz of Wales doesn't escape, he'll presumably get locked up for a while as well, whether in Küstrin or elsewhere, but I don't think no longer G2 would override the military tribunal and demand a death sentence for whoever helped his son. And lastly: longer Fritz of Wales wouldn't invade Silesia in 1740 (since he's not King, no longer G2 is, if their life spans are identical) when Maria Theresia inherits from her father. No longer G2 might or might not - as I said, he was more keen on actual war than FW - but like I said, it's more likely he'd go to war for Jülich/Berg instead. All of which means that while Prussia is probably one of the most important of the German states (especially since Hannover no longer has the British connection) below Austria in the 18th century, it either is on a level with or below Saxony (because Saxony still has Poland, and might make a play for Silesia in 1740 instead of Prussia). Meaning instead of Prussia becoming a European superpower, edging out Austria for most important within the (soon to be former) HRE, dominating all the other German states to the point that when German unification happens in the late 19th century, it's a Prussification, it could be Saxony instead. Or not, and Austria remains where it's at. There are just too many variables to say. But even if it is Saxony, like I said, "Prussian" mentality never develops. Yay?
Kingdom Swap 2: Stanislas I. Poniatowski (Poland) swaps with Joseph II (HRE)
Poniatowski does just fine as Holy Roman Emperor, I should think. He's reform minded, but not nearly as stubborn and my way or the high way set as Joseph, meaning he will pace his reforms better and thus will be able to keep more of them. He might also do better in the marriage department, though that's speculative, as he was never married in rl, so we don't know how he'd have behaved in an arranged marriage organized for him by other people. Whether or not he'd have clued into the fact that his first wife was actually gay and in love with his sister probably depends on whether or not he'd have fallen in love with her himself, as Poniatowski was able to delude himself considerably when in love. He definitely would not have been as hostile to wife No.2. Given that he wouldn't have been fannish about Frederick the Great and trying to imitate him, I don't think he'd have started the War of the Bavarian Succession. So, all in all: a win for Austria and the HRE!
Now, the truly dicy question is whether Poniatiowski in Joseph's place would have gone for the Polish Partition. If he would have been against it for ethical reasons even if that meant Russia and Prussia get to gain territories on their lonesomes, then together with Maria Theresia's aversion of the idea it would have meant Austria remained out of it (though Poland would still have gotten partitioned). But maybe an Austrian version of Poniatowski would have developed some territorial greed?
Meanwhile in Poland: that's easy. Joseph is absolutely unwilling to budge. He's not going to be dictated to, and certainly not by his ex! And he doesn't care whether you want his reforms or not, Polish nobility, you are going to get them! Also? Catholic Church, prepare to have any monasteries and nunneries close that don't also perform social duties (i.e. hospitals and the like). Oh, and there will be state schools, instead of Church run schools.
=> Joseph doesn't survive the year as King of Poland. Whether he'll be assassinated by his fellow Poles or by the Russians is up for debate.
Kingdom, err, Realm Swap 3: Peter the Great (Russia) swaps with Gian Gastone de' Medici (Tuscany)
(Gian Gastone was born in 1671, Peter in 1672, i.e. they were almost exact contemporaries. If you're wondering who Gian Gastone was, I wouldn't blame you, I didn't know about him until a few years ago, either: you can read about the last Medici here)
Gian Gastone loses feuding parents and especially a bigotted Dad but gains a different childhood trauma through the swap. He never has the energy to take power from his older sister and is content to remain a nominal Czar along with brother Ivan while Sofia does the actual governing, while he drinks and parties and is as out and gay as you can possibly be in that place and time. Sofia might not bother to depose or kill him - why should she, if he's content to be a puppet Czar - and would probably be a competent ruler, but Russia would not get dragged screaming into the (then) modern world. I don't think Sofia would go to war with Sweden, so no idea what that means for Karl XII. No St. Peterburg/Leningrad/St. Petersburg, of course. War with the Ottomans is probably on regardless. But Russia's involvment in European affairs doesn't happen until later. I think it would still become a superpower - the sheer land mass and population size makes it inevitable - but if Sofia doesn't change the sort of medieval state, or not to a great degree, it might take much longer.
Meanwhile in Tuscany: No joy for the Ruspanti. Otoh, Tuscany after decades of bigotry and decline under Cosimo III experiences a radical reawakening, so radical the Pope in Rome might feel threatened. Peter radically reforms the Duchy, which includes creating an army, see, and if he treats his Catholic clergy the way he treated the Orthodox clergy in rl... but then the Pope doesn't have real power anymore. Otoh, all the other European powers active in Italy - France, Spain, Savoy, Austria - are getting ever more worried, too, escpecially once Peter starts to hire mercenaries. (There are only so many recruits you can get in Tuscany.) If Peter, like Gian Gastone, is the son of a Bourbon Princess, he's going to do a Louis XIV and use that as an excuse for invading to gain territory, especially once Louis XIV's son and grandsons start to die like flies, leaving only kid future Louis XV (OR IS HE). Peter will probably end up excommunicated, but he just might manage to consolidate various Italian principalities into a sort of nation state before he's done.
...a lot of people won't survive that. Including family members, probably, I think that's inevitable with Peter. And Voltaire will definitely write his biography.
Now, what thornyrose42 wrote to me was: I was listening to a podcast (You’re Dead to Me) where a comedian quipped that Peter III of Russia and Frederick the Great would have both been quite satisfied with a kingdom swap, since Peter admired Prussia so much and Frederick would not have said no to such a giant hunk of Empire.
Whether or not that is true, what do you think would be some of the best and worst kingdom swaps from your favourite periods? Whose style of governance was much better suited to another kingdom’s problems? Who managed where they were ruling but would have floundered when forced to deal with someone else’s political brew.
Peter III will use the Prussian army to go to war with Denmark because of his Holstein inheritance (as he wanted in RL with the Russian army before being deposed and killed). The Prussian army would be up to it in terms of military strength (provided until the swap, all has gone as it did in rl), but somehow I doubt Peter would be, as supreme commander. Hard to say, though, given the sixth months he ruled in rl didn't show how badly or well he'd do in that capacity (well, other than his decision to pull out of the 7 Years War, hand back the Russian conquests to Frederick and expect the Russian army to then happily invade Denmark for him, which was a no brainer). Also, I don't think Britain would be happy with Prussia engaging Denmark a century before schedule, either. Meanwhile, Denmark actually has competent ministers, if not Kings. Basically, that war ends either as a draw for that reason or as a defeat. Peter also doesn't have Frederick's charisma or PR talent of branding himself the champion of the Protestants (when it suits him) or the oppressed (ditto). His wife won't stage a coup against him, not least because Prussia doesn't allow female rule.... but his brothers might.
Meanwhile, Russia: essentially you get a male version of Catherine. (II, of course.) The one department where I have some doubts is that Catherine was smart enough to reassure everyone she's really really sincere with her conversion to the Russian Orthodox faith even when she was a teenager, whereas Frederick might have marketed himself as defender of Protestants when it was useful for war propaganda but never ever claimed to be religious himself, au contraire. And being an open Deist with disdain for Orthodoxy would not have gone down well in Russia. (Peter the Great was a Russian Russian, not a German import like Peter III was and Frederick would have been, and his arguing with the Orthodox still caused him a lot of problems.) Then again, Frederick was a survivor and a good liar, so he might have simply drawn the same conclusion Catherine did and professed sincere orthodoxy. In that case, there are no historical changes for Russia in Frederick's life time, it goes the same it did under Catherine, wars with the Ottoman and Polition partitions included. Also the half hearted attempt to liberate the serfs and then drawing back from it for identical reasons. So, no change there.
The other days
Kingdom Swap 1: Friedrich Wilhelm I. (Prussia) swaps with his first cousin George II (Britain and Hannover)
This fulfills one of FW's dreams, if some of his sidekicks are to be believed. FW as King of Great Britain was an actual possibility for a hot minute, because the childless William of Orange (and III of England) considered adopting him. (They were doubly related.) (This would not have conflicted with the Act of Succession by Parliament settling the English crown on Sophia of Hannover (granddaughter of James I and VI) and her issue, because FW was Sophia's grandson as much as G2. But if William of Orange had adopted him, there would have been no George I (Sophie's son), let alone a G2 (and so forth); the Brits would have gotten a Hohenzollern instead of a Hannover dynasty. (Making G2 the King in Prussia, otoh, has no logical AU explanation, but never mind, we're in it for the crack and the fun.) In our timeline, FW and cousin G2 loathed each other ever since they were boys and FW, despite being a few years younger, managed to beat no longer future G2 up. This set the tone for their entire relationship, which included such highlights as George marrying FW's first crush, the two of them almost fighting a personal combat style duel as monarchs in 1729 and the interminable marriage negotiations between their two oldest kids which contributed to the disastrous escape attempt of future Frederick the Great.
How would it have worked out if they'd swapped kingdoms: welllllll. On the one hand, FW might have been an awful human being, but he was one of the hardest workers ever to sit on a throne. There's a reason why even today, you have some historians making the case that in terms of his "interior" politics (not sure that's the right word for Innenpolitik), he was the best King Prussia ever had, including his son (i.e. Frederick the Great). (This also says something about the not so great Prussian Kings that came later, and then the Emperors, good lord, the Emperors, of course.) He took over a newly declared kingdom and former duchy and barony in considerable financial distress, which consisted of a couple of territories with no shared border, and left it financially and economically sound, with a well filled treasury, lots of new schools and hospitals founded (and state-financed), not to mention that he was the monarch to make school attendance obligatory. And for all that he had a fetish for the military (to put it mildly), he actually was not repeat, not set on starting actual wars. (As a young man, he participated in one of the bloodiest battles in European history after the Thirty Years War and before WWI, the battle of Malplaquet, which was part of the War of the Spanish Succession. This is believed to be the cause of him not starting any wars of his own but only providing his perfectly drilled troops for the various pan-European Wars like the one of the Polish Succession where they fought as part of the HRE (to simplify it). And he wasn't a hypocrite with his austerity programs; he cut down all court expenses and shut down royal residences left by his opulence loving father and grandfather except for a very few. As FW had been the kind of prince who gets a nice bit of real estate and hunting lodge by his parents at age 10 and manages to make it self sufficient and exporting goods by the time he's grown up, freaking out his parents by the fact he's an enthusiastic bookkeeper, I think that trait of his would survive any transplant.
On the other hand: that temper. Good lord, that temper. I mean, the Hannover Georges weren't wonders of stoicism, either, and the father and son loathing through the generations would remain equal, but none of the Georges were throwing their teachers down the stairs before they reached puberty. I think FW would do badly with the whole (relatively new, post Glorious Revolution) constitutional monarch part. Convinced he knew best, he would: lecture the Archbishop of Canterbury on how to be a proper Protestant (none of that High Church Popery for FW!), tell Parliament he had a couple of laws envisioned they really needed to pass, and piss off the entire English nobility on every level in record time. As it was, the Brits were very snobbish indeed about the Hannover. (G1 wasn't a brilliant mind, but he had the avarage continental prince education, meaning he was fluent in French in addition to German, and could make conversation in Italian and Dutch, and had enough Latin to talk with some of his English ministers in it who of course could speak neither German nor French (properly) at the start. How does this show up in English memoirs? As complaints he didn't any languages. Meaning he didn't speak English.) And the Hannover cousins were trying to fit in, and bringing your avarage baroque and Rokoko expense willingness to the table. FW would have shut any royal residences in and around London safe for two (one for summer, one in town for winter), he would have expected the nobility to provide at least one son each for the army and otherwise to develop a work for the state mentality, he'd have ignored balls and sure as hell wouldn't have organized some, and while he actually liked Händel, his idea of enjoying Händel's compositions in rl was to let them be played by army musicians (to save money). He sure as hell wouldn't have sponsored any opera performances. As for the sciences, he'd have seen the sense in encouraging medical developments and anything that's useful for economics, farming, import/export, but more abstract mathematics? Art? Nah. Oh, and anyone male and tall from the Orkney islands to the southern most part of Cornwall, not to mention the Colonies, should be prepared to get kidnapped so he can serve in FW's personal regiment of Windsor Giants.
So, my guess is: after only a few years of FW, both Whigs and Tories get together to conspire with the Queen to use his next big fit of temper to declare him insane and have a Regency installed.
Meanwhile in Prussia: (No longer) G2 is an okay King for the era. No idea whether he manages to make Prussia solvent, let alone fill the treasury, but the Hannovers weren't doing badly, economy wise, while still being Princes Elector, pre Britain, so let's say he does, if not to the same extent, and far slower. He might actually go to war about Jülich/Berg (don't ask, it's an eternal claim and grudge thing for generations of German monarchs), though, since participating in the same War of the Spanish Succession FW did (also just in a single battle, though a different one) left him wanting more, not less. What he most certainly does not manage, though, is creating what people think of when they talk about "Prussian mentality". His wife, Caroline, as Queen is far more socially and culturally active than FW's wife Sophia Dorothea was, and since her marriage with George is very different from the FW/SD disaster, she gets the necessary budget to continue her mentor Sophia Charlotte's "Athens on the Spree" project. The Berlin Academy florishes. (The overall economy might not, or at least not to the same degree.) No longer G2 has the same awful relationship with his oldest son as he did in rl because that's how Hannovers (and Hohenzollern) roll, so we still might get a Prussian Crown Prince escape attempt (or successful escape?) around 1730. If no longer Fritz of Wales doesn't escape, he'll presumably get locked up for a while as well, whether in Küstrin or elsewhere, but I don't think no longer G2 would override the military tribunal and demand a death sentence for whoever helped his son. And lastly: longer Fritz of Wales wouldn't invade Silesia in 1740 (since he's not King, no longer G2 is, if their life spans are identical) when Maria Theresia inherits from her father. No longer G2 might or might not - as I said, he was more keen on actual war than FW - but like I said, it's more likely he'd go to war for Jülich/Berg instead. All of which means that while Prussia is probably one of the most important of the German states (especially since Hannover no longer has the British connection) below Austria in the 18th century, it either is on a level with or below Saxony (because Saxony still has Poland, and might make a play for Silesia in 1740 instead of Prussia). Meaning instead of Prussia becoming a European superpower, edging out Austria for most important within the (soon to be former) HRE, dominating all the other German states to the point that when German unification happens in the late 19th century, it's a Prussification, it could be Saxony instead. Or not, and Austria remains where it's at. There are just too many variables to say. But even if it is Saxony, like I said, "Prussian" mentality never develops. Yay?
Kingdom Swap 2: Stanislas I. Poniatowski (Poland) swaps with Joseph II (HRE)
Poniatowski does just fine as Holy Roman Emperor, I should think. He's reform minded, but not nearly as stubborn and my way or the high way set as Joseph, meaning he will pace his reforms better and thus will be able to keep more of them. He might also do better in the marriage department, though that's speculative, as he was never married in rl, so we don't know how he'd have behaved in an arranged marriage organized for him by other people. Whether or not he'd have clued into the fact that his first wife was actually gay and in love with his sister probably depends on whether or not he'd have fallen in love with her himself, as Poniatowski was able to delude himself considerably when in love. He definitely would not have been as hostile to wife No.2. Given that he wouldn't have been fannish about Frederick the Great and trying to imitate him, I don't think he'd have started the War of the Bavarian Succession. So, all in all: a win for Austria and the HRE!
Now, the truly dicy question is whether Poniatiowski in Joseph's place would have gone for the Polish Partition. If he would have been against it for ethical reasons even if that meant Russia and Prussia get to gain territories on their lonesomes, then together with Maria Theresia's aversion of the idea it would have meant Austria remained out of it (though Poland would still have gotten partitioned). But maybe an Austrian version of Poniatowski would have developed some territorial greed?
Meanwhile in Poland: that's easy. Joseph is absolutely unwilling to budge. He's not going to be dictated to, and certainly not by his ex! And he doesn't care whether you want his reforms or not, Polish nobility, you are going to get them! Also? Catholic Church, prepare to have any monasteries and nunneries close that don't also perform social duties (i.e. hospitals and the like). Oh, and there will be state schools, instead of Church run schools.
=> Joseph doesn't survive the year as King of Poland. Whether he'll be assassinated by his fellow Poles or by the Russians is up for debate.
Kingdom, err, Realm Swap 3: Peter the Great (Russia) swaps with Gian Gastone de' Medici (Tuscany)
(Gian Gastone was born in 1671, Peter in 1672, i.e. they were almost exact contemporaries. If you're wondering who Gian Gastone was, I wouldn't blame you, I didn't know about him until a few years ago, either: you can read about the last Medici here)
Gian Gastone loses feuding parents and especially a bigotted Dad but gains a different childhood trauma through the swap. He never has the energy to take power from his older sister and is content to remain a nominal Czar along with brother Ivan while Sofia does the actual governing, while he drinks and parties and is as out and gay as you can possibly be in that place and time. Sofia might not bother to depose or kill him - why should she, if he's content to be a puppet Czar - and would probably be a competent ruler, but Russia would not get dragged screaming into the (then) modern world. I don't think Sofia would go to war with Sweden, so no idea what that means for Karl XII. No St. Peterburg/Leningrad/St. Petersburg, of course. War with the Ottomans is probably on regardless. But Russia's involvment in European affairs doesn't happen until later. I think it would still become a superpower - the sheer land mass and population size makes it inevitable - but if Sofia doesn't change the sort of medieval state, or not to a great degree, it might take much longer.
Meanwhile in Tuscany: No joy for the Ruspanti. Otoh, Tuscany after decades of bigotry and decline under Cosimo III experiences a radical reawakening, so radical the Pope in Rome might feel threatened. Peter radically reforms the Duchy, which includes creating an army, see, and if he treats his Catholic clergy the way he treated the Orthodox clergy in rl... but then the Pope doesn't have real power anymore. Otoh, all the other European powers active in Italy - France, Spain, Savoy, Austria - are getting ever more worried, too, escpecially once Peter starts to hire mercenaries. (There are only so many recruits you can get in Tuscany.) If Peter, like Gian Gastone, is the son of a Bourbon Princess, he's going to do a Louis XIV and use that as an excuse for invading to gain territory, especially once Louis XIV's son and grandsons start to die like flies, leaving only kid future Louis XV (OR IS HE). Peter will probably end up excommunicated, but he just might manage to consolidate various Italian principalities into a sort of nation state before he's done.
...a lot of people won't survive that. Including family members, probably, I think that's inevitable with Peter. And Voltaire will definitely write his biography.
Now, what thornyrose42 wrote to me was: I was listening to a podcast (You’re Dead to Me) where a comedian quipped that Peter III of Russia and Frederick the Great would have both been quite satisfied with a kingdom swap, since Peter admired Prussia so much and Frederick would not have said no to such a giant hunk of Empire.
Whether or not that is true, what do you think would be some of the best and worst kingdom swaps from your favourite periods? Whose style of governance was much better suited to another kingdom’s problems? Who managed where they were ruling but would have floundered when forced to deal with someone else’s political brew.
Peter III will use the Prussian army to go to war with Denmark because of his Holstein inheritance (as he wanted in RL with the Russian army before being deposed and killed). The Prussian army would be up to it in terms of military strength (provided until the swap, all has gone as it did in rl), but somehow I doubt Peter would be, as supreme commander. Hard to say, though, given the sixth months he ruled in rl didn't show how badly or well he'd do in that capacity (well, other than his decision to pull out of the 7 Years War, hand back the Russian conquests to Frederick and expect the Russian army to then happily invade Denmark for him, which was a no brainer). Also, I don't think Britain would be happy with Prussia engaging Denmark a century before schedule, either. Meanwhile, Denmark actually has competent ministers, if not Kings. Basically, that war ends either as a draw for that reason or as a defeat. Peter also doesn't have Frederick's charisma or PR talent of branding himself the champion of the Protestants (when it suits him) or the oppressed (ditto). His wife won't stage a coup against him, not least because Prussia doesn't allow female rule.... but his brothers might.
Meanwhile, Russia: essentially you get a male version of Catherine. (II, of course.) The one department where I have some doubts is that Catherine was smart enough to reassure everyone she's really really sincere with her conversion to the Russian Orthodox faith even when she was a teenager, whereas Frederick might have marketed himself as defender of Protestants when it was useful for war propaganda but never ever claimed to be religious himself, au contraire. And being an open Deist with disdain for Orthodoxy would not have gone down well in Russia. (Peter the Great was a Russian Russian, not a German import like Peter III was and Frederick would have been, and his arguing with the Orthodox still caused him a lot of problems.) Then again, Frederick was a survivor and a good liar, so he might have simply drawn the same conclusion Catherine did and professed sincere orthodoxy. In that case, there are no historical changes for Russia in Frederick's life time, it goes the same it did under Catherine, wars with the Ottoman and Polition partitions included. Also the half hearted attempt to liberate the serfs and then drawing back from it for identical reasons. So, no change there.
The other days