Hitler was the ultimate nationalist.
No, actually he was not, he was a PAn-German ethnic racist, quite the opposite of a Nationalist.
A nationalist respects the differences of various nations, like the Netherlands, Austria, the Sudetenland, Poland, etc, but Hitler had no respect for any of that, or any borders either.
In his mind if you spoke a Germanic language then you belonged in Germany, and if you spoke a Slavic language then you deserved nothing more than to be a serf to the superior Germanic people.
That is not nationalism, it is leftwing Eugenics posing as nationalism.
Hitler was an anti-Borders Leftwing Socialist, nothing more.