In the case of the USA, the nation = the empire. The same equation is likely to apply to the other rich nations (Germany, Japan, France, the U.K., etc.), though less clearly & more ambiguously, for nationalisms of second-rate empires may sometimes assume the form of anti-Americanism & hence anti-imperialism of sorts (e.g., the political consciousness & language of Okinawans who have struggled against both the U.S. military & the Japanese government).
As for the rest of the world, nationalism may be a qualified good -- though never without a multitude of problems which always accompany it materially & ideologically -- *if* it represents a thrust from below with a high degree of working-class content not just in language but in actually implemented political programs (e.g., land to the tillers).
The most valuable forms of anti-colonial & anti-neo-colonial nationalisms, however, have been products of cosmopolitan dialectics of colonies & metropolises, with future anti-colonial leaders of the masses educated & radicalized in metropolises as well as building political networks in the wider world. Recall Simon Bolivar & the influence of French political philosophers upon him. Read Paul Gilroy, _The Black Atlantic: Modernity and Double Consciousness_, Cambridge: Harvard UP, 1992; Robin D.G. Kelley, "A Poetics of Anticolonialism," at _Monthly Review_ 51.6, at <http://www.monthlyreview.org/1199kell.htm>; etc.
The best representatives of nationalisms on the Left have never been parochial & provincial....
Yoshie
Postscript: And remember Tom Paine, a radical commoner of the world, a defender of the French Revolution!