>Both the Soviet Union and Nazi Germany called themselves socialist, and both claimed to be doing what was best for their people.
The Nazis weren't socialist. They appropriated the term as a propaganda tactic, a means of appealing to the masses. North Korea calls itself a democratic republic, but is obviously neither. One can't simply assume political labels to be correct. In terms of their actual policies and beliefs, the Nazis were vehemently anti-socialist.
One could argue fascism is a subset of populism.