Is National Socialism just Nationalism + Socialism?

No. National Socialism is the English translation for the German word “Nationalsozialismus”. The translation “National Socialism” does not capture the true meaning conveyed in the German original. It isn’t totally inaccurate either, but it is best to understand the worldview as just Nationalsocialism. The “National” can not be thought of as an adjective for the “-socialism”. As in many other contexts, here also, the whole is greater than its parts. Nationalsocialism is not connected to Marxist ideas of Socialism.