At the least, Virginia would be renamed
I think an interesting novel would be one in which Catherine of Aragon gave birth to a healthy son, instead of a healthy daughter. Because it would be a ridiculously simple and plausible change in the way the world worked out (unlike, say, Charles Lindberg running for President), but could completely change the course of Western history. No Anglicanism, so probably no English involvement in the Netherlands, no English Civil War, no Spanish Armada, no Puritanical Plymouth Colony. Nothing. Heck, it's entirely possible (keeping in mind I don't know nearly enough about the topic) that the Treaty of Westphalia, the framework for the last 300 years of diplomacy, would never been signed had England not supported the Netherlands and thereby lengthened the war out to Eighty Years.
Of course, that leads to the question of what the world would end up being like if you essentially were forced to rewrite the history of the dominant power of the 18th Century two hundred years before it became Super Important. But that's probably what the fun is about. Did Spain move north from Florida and take over North America as well as South? Were the congealing protestant principalities in Germany crushed? Did Shakespeare write MacBeth, not having James I to make side-references to? Who knows?
... Yes, I'm doing a paper on England in the 17th Century. No, this little free-write side-rant didn't help at all. Why do you ask?
I just named a paper after the first Buffy Season Finale, using a very subtle one-letter pun. If I'm very very lucky, Gillespie is a fan.