Theme Suggestions For Variable Win Conditions Game

This could apply to any sort of theme, ranging from neighborhood lemonade stands to global thermonuclear war.

Any idea of the theme you're trying to include? Or is this wide open?

As LOS said, there are a lot of candidates here.

You could have a more cut-throat version of Villainous that allows you to actually attack opponents. Could be a mafia theme, supervillains, etc.

Maybe the successors to a failed state trying to set up their visions of utopia. Could be a political theme, warfare theme, post-apocalyptic theme, etc.

Colonization seems possible, though you'd need to explain why the factions can't simply fan out and avoid each other. Maybe this is the only habitable planet after Earth was lost. Or it is Earth and the aliens lost their world (like the Defiance series).

Could be Ways of Thought trying to persuade the masses, which can skew religious, scientific, social, etc. One example was the backstory to the RPGs Mage: The Ascension and Mage: The Sorcerer's Crusade.

Lots of possibilities.

Your mechanics immediately made me think of the DC deckbuilder game. Check it out if you haven't. I also agree with the other posters. any theme can fit with this. The better question is, what kind of feeling do you want this game to have? A serious/action feel, dramatic story-telling? Maybe comedy or dark humor?

Deciding on that could help lead you toward a theme that could highlight those sorts of feelings. Also, what theme do you know alot about? I think it's helpful and easier to be more thorough if you use a theme that's already close to your heart.