Well, in European history the answer is because wars and conquest were profit-seeking ventures, and those who managed to amass foreign lands intended to squeeze

Well, in European history the answer is because wars and conquest were profit-seeking ventures, and those who managed to amass foreign lands intended to squeeze them for as much profit as possible. It's easy to oppress people you never see, who are just numbers in a ledger. People you see every day and must rule face to face is another matter.