Example with a context:
Putin is a nationalist, but it's ultimately a state nationalism, it's about the Russian federation.
Why do you think state nationalism in this situation is used with an article as though it's a thing that can be counted? Don't you think that if we get rid of the article completely, the sentence will sound grammatically better? As you know, nationalism, much like other forms of isms, is intrinsically not a countable thing, so how can you possibly place an article in front of it? Please help me clear things up a little bit here.