Trying to put Nazi Germany into a simple box of nationalism or imperialism isn't a good idea, but German motives were more nationalist than imperialistic. Nazi ideology planned on uniting Germans (this explains their expansion into regions like Austria, the Sudetenland (home to Sudeten Germans), and Danzig, at the time the Free City of Danzig, which was majority German) which gave them an excuse to "liberate" the Polish corridor (including Danzig) between the main German country and East Prussia (modern Kaliningrad). However, German expansion was not just going to stop at what was considered ethnically German, encouraging a pull of German settlers to eastern Slavic lands. This is linked to the idea of Blood and Soil (an idealized German/Nordic farm life) and of course Lebensraum, which called for pushing native Slavs (considered untermenschen or subhuman) off of their lands to be replaced by German settlers who use the land to grow crops to feed Germany. Taking all that into consideration, creation of an empire or imperialism was probably not the goal of the German state. Uniting Germans and then eventually expanding heavily to support this Germanic state was the end goal, which would hint more towards nationalism with strong ethnonationalist tones.