I am no fan of nationalism but I have to acknowledge it has some function as a transitional state. It works as a mean to get disparate groups to unify without conquest and complete cultural destruction or genocide of the joining group of the infamous "kill the men, rape the women, enslave the children" style.

Nationalism has its own infamous issues of course and is more of a lesser evil than a good. Bypassing it would be nice but I don't know of any successful cases doing so.