Humans evolved to cooperate within their tribe. Everyone else is an outsider, who you might trade and cooperate with, but you might also fight. All depends. At

Humans evolved to cooperate within their tribe. Everyone else is an outsider, who you might trade and cooperate with, but you might also fight. All depends. At any rate, the history of civilization has lots of conquests and empires. Once an empire is established, forced cooperation also happens, until it doesn't.