Why did more nationalist movements rise after
World War II?

During wwii, for the most part, everyone was united. we were all fighting for one cause. after wwii, america has sealed its fate as a global presence. we took on a leadership role of sorts in the playing field. then, the cold war happened (to sum it up, america and russia were not very happy with each other). when the cold war came about, things like the space race showed up too (first to go to space, first to land on the moon, etc). there were so many goals that each nation was working towards to make itself better, to make itself known, and to make sure they were a force to reckon with. in order to do that, you had to have people that were willing to do that. more people wanted their country to become a superpower, or launch people into space, or have the best weapons. people wanted to be proud of their country. hopefully that helps you :D