Why have the majority of past civilizations been patriarchies? Neither the Roman or Greek empires had equal rights for women. It seems egalitarian nations seem to be a fairly new concept.
It was caused by the advent of agriculture, because in hunter-gathrer societies the division of labour was even, while in agricultural societies men got more power and privileges. Because of food surplus many things happened - women could have more children, which caused them to stay at home and become housekeepers, while the whole society stratified by wealth, which gave men even more power.