What would happen if there were no borders?

If there were no borders, there would be erratic and unpredicted behaviours everywhere. Looking back in past, Babylon, ancient Greece, Roman Empire, feudal England and now in not so distant future, the world was always divided in countries, and every one of them had their own set of regulations, culture etc. Some of them were more similar than others, but nevertheless there were differences. If there were no borders, there would be no effective authority to ensure order and laws that are equal to all, and without unique rules for all there would be injustice, chaos, anarchy even. In the USA there are people that say they are ''citizens of the world'' and by that they are stating that no country is above them beause they are ''free'' from borders, USA politics, their laws etc. Now imagine if every person started acting chaotic, denying every rule they have been taught just because they feel like no law applies to them because they are not bound by the borders of that or any state. Living in cohezion between all the people in the world is just a fantasy because there are too many differences in cultures and people's mindsets.