Women and religion.
I'm getting past the point now of believing that it's simply men's interpretation of their holy books that's the issue, and not the foundational texts of their faiths that are also at fault. To paraphrase the US-based Freedom from Religion Foundation: the Bible itself is a handbook for the subjugation of women. But then the Bible, like religion, was created by men for men, and has been used ever since its inception as a tool to keep women in their place.