Unity is such a powerful word to use if you're in a group. Such as conflicts that make us connected and in locked arms with each other. In such a way to make us, and consider ourselves as one, they break the molds and differences between us when everyone is in the same situation.
I can't imagine a world without unity when a devastating event happens where everyone is affected. That's not as impossible as you think, there must have been some history between these worlds where no one cooperated or united after a devastating event that crumbled both sides. There must have been at least one in history that might have avoided being united since sometimes doing and fixing your own mess despite a similar situation could help if the two are that different in the way they live.
I guess we'll never know. For now, I like the way how things are right now. But currently, everyone needs to address the biggest fish in the pond.