Patriarchy is a social system that is about more than just power differentials between men and women. As it arose (around the time of the agricultural revolution) was the first time that we began to see wealth disparity, class systems, and other sorts of dominance hierarchy elements.
This excerpt from an article in The World Economic Forum is a little bit oversimplified, because agriculture does not automatically equal a shift from egalitarianism, but it did eventually turn out this way and it's a good shorthand primer to a complex question.
"Labor roles became more gendered as well. Generally, men did the majority of the fieldwork while women were relegated to child-rearing and household work. Without contributing food (and by association, without control over it), women became second-class citizens. Women also had babies more frequently, on average once every two years rather than once every four in hunter-gatherer societies.
Because somebody had to have control over surplus food, it became necessary to divide society into roles that supported this hierarchy. The roles of an administrator, a servant, a priest, and a soldier were invented. The soldier was especially important because agriculture was so unsustainable compared to hunting and gathering. The fickleness of agriculture ironically encouraged more migration into neighboring lands in search of more resources and warfare with neighboring groups. Capturing slaves was also important since farming was hard work, and more people were working in these new roles.
This division of labor and social inequality had very real consequences. For instance, while the majority of people had disastrous health compared to their hunter-gatherer ancestors, the skeletons of Mycenean royalty had better teeth and were three inches taller than their subjects. Chilean mummies from A.D. 1000 had a fourfold lower rate of bone lesions caused by disease than commoners."
In other words, patriarchy arose somewhat organically in response to changing social conditions. It wasn't some Machiavellian evil plot, but nonetheless, it is a dominance based system that was maintained through coercion and threat of violence - towards women but also towards other "weaker" men. And, it continued to be upheld with laws and customs primarily made by men for thousands of years afterwards. In case you've forgotten, there were laws on the books a mere 50 years ago that kept women from having the same opportunities as men. Women do uphold patriarchy in many ways, but acting like women really had free choice all along and could have just changed the system if they'd only been really responsible for their own actions is just not in touch with historical reality.
