He had to go to Russia , there was no choice, war was getting longer and he needed OIL from central europe. After invading Poland war with Soviets was ineviteable, he just took the initiative of first strike.
Secondly he broke the treaty with Stalin by invading Poland.
Lets get the numbers right. Soviet union lost maximum people in WW2. google it if you don't agree.
close to 2 crore.
Hitler did blunders which an Army general will never do.
1. Could have allowed 1.5 lac troops to return from Stalingrad, he already had the oil fields in central Russia under him.
ended up loosing all (90,000 surrendered).
2. After inflicting heavy casualty on England and capturing France, he should have agreed to talk about peace and in return could have become part of the western group which hated Soviet union for communist, America would have supported Hitler.
3. His personal vengeance against Jews took over the national interest, else America could have swung in German favor.
4. He had little political advisors and very small political brain to capitalize the situation.