Nationalism is government in the national interest

Westerners have been demonising nationalism since WW2 because Hitler and Mussolini identified themselves with nationalism. 

If nationalism means government is in the national interest, it would appear that neither Hitler nor Mussolini understood the concept. German and Italian expansionism was the cause of war and all empires are acquired by war, including the Spanish, British and American global empires.  

Perhaps It would be more accurate to say that the failure of German and Italian nationalism was a failure of diplomacy or failure to recognise the limitations of their own armed forces as well as the mistaken expectation that Britain would be reasonable about Germany moving around in its own backyard.