A lot of people ask me about the themes present in my writing. Of course there are themes relating to gender, race, and sexuality - I'm not sure it would be possible for me to write fiction without those themes.
But if I were to identify the core theme in my writing - the one theme that is consistent throughout the 6 novels I've finished, and just about every novel that I have planned (more than a few,) it would be the theme of what happens when people of sometimes subtly, and sometimes greatly different cultures (and I mean that in the broadest terms - cultures of human beings as well as cultures of aliens) are brought together by necessity.
Here are some examples:
In the first three books of The Casitian Universe series, the primary culture clash is between the Casitians - human beings gone from Earth for five thousand years, having evolved a completely different society, and Earth humans. But there are also other culture clashes - a big culture clash within humans on Earth, as well as cultures of the Galactic Community. These are big - involving many people, and public.
In the fourth novel of the series, the biggest culture clash is small and individual, and not at all public. It is between a Casitian and US society in the mid-19th century. There is, described in that novel, the big, public culture clash at the time - between southern slave society culture, and northern culture that abhored slavery.
In the novel I just finished, it's all very different, since none of the societies that I describe are familiar - but it is a clash between two cultures, both conservative and tradition-focused, but they manifest that in completely different ways.
I enjoy writing about this - it's a big question for me in life in general. How do we learn how to encounter other cultures in such a way as to be able to accept those cultures for what they are, and not in any way decrease the value of our own culture, or denigrate what others do. It's an interesting challenge, for sure.