Maybe some cultures can team up? For example elfs can team up with humans and help in war with others. I know this is kinda stupid idea but why not?

Races can ally under the same coalition...or do you mean have an option for Human race to capture elven village and then during another war it will have humans and elves fighting for that conquering faction?

sorry didn't play update much, I never knew they made so they can be in one coliation