I've noted that the left hates boundaries - at least the kind that allow people to say "no" to them.
They hate the fact that there is a boundary at all, and work to eradicate it by expanding their reach until everything is inside said boundary, and thus, effectively, there are none
Sure, some "nationalists" don't respect the rights of others to have their own nations and sovereignty. They are also truly imperialists. But a nation that just wants self-determination is not by necessity an empire, trying to rule the world or as much of it as they can control.
A globalist system has to be.