Humans may need to leave Earth to survive extinction. Is cultural homogenization necessary for us to achieve the means to facilitate this?

It's hard enough to get countries to align on policy just living on Earth, and many times it doesn't happen. Additionally, the double edged sword is that we want to align on certain items, yet regarding other items we want to retain cultural distinction (and both of these aspirations are perceived as appropriate!). Humans are deeply attached to their unique identity among humanity, and the unending parade of wars exemplifies this. So regarding my question, most people enormously underestimate the level of global cooperation that will be needed to lift all of humanity off the planet and sustain it elsewhere. But if in, say, one thousand years, brought on by technological advancements birthed in the current few hundred years we're in the middle of, we all end up light brown and all part of one global culture ("I'm from Earth, Sector 824"), where countries are extinct, then maybe the psychological foundation of the unified cultural identity that I think we'll need for space colonization will be in place, and we can then do it. Without this change, I personally don't see it happening. What do you think?