Re: Ahem, everyone voting on (almost) everything does exist....
I recognized there are exceptions to the rule; just noting the broad trend.
"In other parts of the world, different patterns have emerged. The largely Spanish oriented nations of South America have experienced wars between nations and murderous conflicts within nations which to the outside eye seem fairly homogenous;"
Like I said, exceptions to the rule. Up north around Colombia and in Central America, a lot of the violence is gang-related and stemming around the drug trade: hot-leaded competition for a lucrative resource. Towards the center most of the beef is based on political power struggles: again with the top spot at stake things can get heated at times, but they usually don't flare up that often or for that long.
"Pakistan might be seen as more homogenous and also more violent than perhaps India"
As I recall, Pakistan is also organized more tribally than in India. It's less hierarchical, less centralized, and it's one reason it's so difficult to cement a central authority in there or Iraq or plenty of other places as tribal organization tends to be more autonomous than what we're used to in the West. In other words, they're not used to running things Western style. Furthermore, I don't recall many of these tribes to be as homogeneous amongst themselves as we are led to believe, which is why disagreements between them are the norm rather than the exception.
As for the American Civil war, it was both cultural AND societal differences that caused it. The industrial North and agricultural South had diverged significantly since the War for Independence, to the effect each had a uniquely-identifiable culture (which we can still see today, y'all). Throw in a stark political contrast over the distribution of authority and just a smidgen of disagreement over people's rights and it kinda blew up in South Carolina in 1861.