After winning a few games, I've noticed that if I ally with a race or two early in the game and then destroy the rest of the races it counts as a political victory, even if my ally didn't partake in the war. I see how this could be classed as a political victory, since I did have an ally to ease the game, but if most of the game was played in hardfought wars it's a little annoying to only get a political victory for, essentially, winning the game via military power.
I know, I could always break the alliances and then crush my former allies too, but that just adds extra turns that would be pointless.
Just throwing this out for comments.