Many Native-American tribes practiced some form of slavery before the European introduction of African slavery into North America.
https://en.wikipedia.org/wiki/Slavery_among_Native_Americans_in_the_United_States
There's such reverence for Native Americans on the Left.
The 2020 Democratic Party Platform begins by acknowledging, honoring, and paying respects to the Tribal Nations and Indigenous peoples who have existed "here since time immemorial".
https://www.demconvention.com/wp-content/uploads/2020/08/2020-07-31-Democratic-Party-Platform-For-Distribution.pdf
There's a narrative on the Left about how White Supremacy came to North America, how White civilizations introduced both genocide and slavery to lands that were supposed to have previously been occupied by more innocent types of nonwhite humans who lived in accord with each other and with nature.
The historical record does not show that the First Peoples were generally more peaceful and egalitarian than other groups of humans. They fought wars, they captured and traded slaves, they practiced torture.
The main differences between the European colonists and the First Peoples who preceded them were these two: (1) Europeans had tougher immune systems because they'd been exposed to more diseases, diseases that practically wiped out the First Peoples upon exposure; and (2) Europeans had deadlier weapons technologies.
Otherwise, we were all humans, all members of the same species, all descendants of the same Mitochondrial Eve who lived in Sub-Saharan Africa around 150,000 years ago.
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The main reason we humans do not continue to endorse legalized slavery in the 21st Century is because we have ubiquitous labor-saving machines powered by fossil fuels that are cheaper to own and operate than slaves. Slavery, serfdom, and similar caste systems have been widespread throughout human history. But slavery became economically inefficient during the 19th Century.
We ignore history when we presume that White Supremacy is somehow different from how any set of humans have operated. When one class of humans has power over another class, they oppress them. It's human nature.
These class systems operate differently among capitalists, and differently among socialists, but they persist. Our ideologies and justifications are endlessly creative -- why one group of humans should have more power and more wealth than another.
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There have also always been counter-ideologies -- that everybody should be treated fairly, that leaders should serve at the pleasure of the led, that resources should be shared, that neighbors in need should be welcomed and cared for, that humans should live in harmony with nature.
I can add my weight to these counter-ideologies in the 21st Century, but I have no illusion that my side will win. Especially when my side tells lies to itself about human history and human nature.