I don't think the social status of Africans in the US is inconsistent with my hypothesis. I'm talking about extremely broad political trends since climate manifests itself only over a lot of time (such as generations). Roughly, I'm talking about the susceptibility to liberalism as a deviation from the default of autocracy.

In the US the governmental system was set up by ex-Europeans, so the Africans wouldn't have had a chance to think through what sort of society they wanted in North America. That job was taken. Instead, African Americans had to adapt to being slaves, due to the crimes of European imperialism.

My hypothesis here is too broad a brush to account for the differences between populations within the same geographical region. I'd have to turn to other factors, such as history, culture, and so on. Possibly, genes, penis sizes, or other physiological differences would be relevant, too, but I doubt they'd be significant.