La Marseillaise is undeniably martial. It is not particularly nationalistic, however. It does not extol the virtues of France, it does not affirm territorial claims, it does not attack any other country directly or by allusion. All of these are fairly common in national anthems in the era. By contrast, the central theme here is basically "Fight! ... Because we're really screwed if you don't."

While I don't deny the issues with nationalism, nor that national anthems were a major tool of fomenting such nationalism, I think it improper to assert that La Marseillaise was a major contributing factor to that end.