They weren't "oppressed" — they simply weren't given the same opportunities to do certain tasks, or weren't expected to achieve the same kind of work as men. Those kinds of systems benefitted women in many ways, quite ironically. This was simply a byproduct of the fact that early societies placed great importance on gender roles and a clear social hierarchy. The reason why these societies ended up placing women in certain roles, while leaving other tasks for men, is very simple: biology and evolutionary psychology. Men are better suited physically to certain tasks—hunting, protecting, or heavy labor—while women are good for nurturing and reproduction. Nothing was "unfair" or "oppressive," it was just the way the world worked. These societal rules weren't created with the intention of oppressing half the population, but rather to preserve the structure and longevity of each society. Of course, this was before modern feminism came in and started dismantling the social order—which has led to the rapid deterioration of our society as well as the rise of degeneracy and decadence.