Hitler had this list of peoples to exterminate:
* Jews
* Romanies ("gypsies")
* Slavs (Poles, Russians, Ukrainians, Czechs, modern Macedonians, Serbs, Slovaks, Bulgarians, Slovenians...)
Jews took the biggest blow, but Hitler didn't plan to stop there. And not all of it was even ethnic. For example, he hated homosexuals and disabled people. He was going to clean the race. Communists were a target, too.
The reason he didn't exterminate everyone at the same time is that he needed slaves and collaborators in the transitional period. People down the list could be used to exterminate those higher up (indirectly, but sometimes directly).
https://en.wikipedia.org/wiki/Lebensraum