Globalization is already well underway, our economies are entertwined, our technological advances, our medicine, knowledge, and even entertainment.
There is war, incompatible theologies, racism, hate, and all sorts of stuff that has the appearance of not being "united". As long as humans exist those things will persist. We're not robots, our flaws exist because of the nature of our biology.
I think it's fair from at least this perspective to say we're already united.