Sins of a Solar Empire.
That name is mainly super memorable to me because the only game of it I ever played honestly kinda crushed me.
I made a game with me, an ultra-hard AI as my ally, and 3 medium AI as enemies. I had spent most of the game just advancing in tech and I had small skirmishes here and there but mainly I was just going for a cultural/technological victory. Problem here is, my AI companion was going hard on plotting out how to crush the other AIs, and....well....I forgot to enable the "People in a team are always allies" option, so eventually this AI told me they wished to go Neutral. It was at this point in time where I spent every single resource I had on amassing an armada to go at this ally, but the realization is that I was too late - I had allowed him to become so powerful and never questioned that they might turn on me. The very last moment for me in that game was me directing my armada towards one of his fleets, and I saved the game and then promptly uninstalled it...because I couldn't bare the reality of seeing how it was going to play out.
I already knew I had lost. This was the Sin of my Solar Empire :'(