Some days you're almost sane, and then there are days like this. While the concept of the nation is indeed an important source of cultural identity, it is hardly the only source nor is it even the most important one. "Look to history to get factual basis for that."
Dolt.
J, have you ever met a Sumerian? No. And you never will. You might find someone who can trace their roots back to Hammurabi or Gilgamesh(assuming he's a real person), but you'll never find someone who identifies themselves with that culture.
Chances are, you'll never meet a Zoroastrian either, as there are only 115,000 remaining. Do we know the truth of the Kingdoms of Israel? Only if you believe the Old Testament.
These are important because they show my point. The Assyrians decimated, brutalized and assimilated the earliest Hebrews and Babylonians. Zoroastrianism was all but wiped off the face of the planet when Persia was conquered by Greece, Rome and then the first Muslims.
If you get rid of national borders, in about a hundred to two hundred years, there won't be an American culture or a Chinese culture or a Russian culture or a German culture, etc. They'll be dismantled in the name of universal appeal and assimilated. We'll have one "world" culture, and the rest will go to the museums.
This might be fine for peace, but it'll destroy any strain of unique identity in the world, and, as I've said, lead to a gray, dull, amorphous blob of sameness, and that's boring.