The problem IMO is politics, not nationalism (which only enters into the politics indirectly). European integration is a half-done project. Political forces that want to finish the job get cancelled out by political forces that want to undo the progress we've already made with the net effect of nothing getting done in any direction, maintaining a status-quo that pretty much nobody wants, and nobody (nationalist or otherwise) ever wanted. And that status quo is that doing business in a pan-european way is a bureaucratic hellscape.
The problem IMO is politics, not nationalism (which only enters into the politics indirectly). European integration is a half-done project. Political forces that want to finish the job get cancelled out by political forces that want to undo the progress we've already made with the net effect of nothing getting done in any direction, maintaining a status-quo that pretty much nobody wants, and nobody (nationalist or otherwise) ever wanted. And that status quo is that doing business in a pan-european way is a bureaucratic hellscape.