I like the idea, but I think there would have to be many factors which affect it - Distance, Era, Type of Government, Certain Techs,etc. It's true, America is sort of a rebellion of England. England couldn't manage part of it's empire cause it was too far away, and lost the War of Independence. But as to the culture of the capital always having to be more powerful than any other city in the realm, I don't think it's so simple - look at Canada, for instance, Toronto, Vancouver, and Montreal are way bigger than Ottawa, and nobodies going to be seceding anytime soon. Same with NYC and LA compared to WashingtonDC. Of course, these are very wealthy countries in the modern era, but you see what I mean...