I'm assuming you know about the whole idea of living space, hatred of communism, Judaism, etc.. and are asking why the Germans attacked the Russians before they finished off the west. If not just let me know and I'll be happy to explain it to you.

For the starters the Soviet Union held vast reserves of natural resources that the Germans needed (Oil being a prime example). The Germans had no reason to fear the west as Britain was being bombed into submission and the United States had not entered the war. So for all intensive purposes the Germans had no other enemies. The Germans also wanted to invade Russia as quickly as possible before the Russians could further improve their army, which already outnumbered the German army in nearly every way. The Russians had been badly humiliated by Finland in the Winter War and to outside German observers it appeared as though the Soviet army was weak. Hitler figured they would destroy Russia in less than six months. He was quoted as saying: "one only needs kick in the door, and the whole rotten structure will collapse". So while in hindsight it may appear that Germany made a mistake, back then it appeared to be a good idea.

If you're interested in some more documentaries look up: "the world at war" or "ww2 in colour" both are very good.

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Proper comments for this subreddit should be in-depth, comprehensive, and informative while properly situating the answer in its historical context. It should also be backed by appropriate primary and secondary sources, whether or not explicitly mentioned in the comment (i.e. you should always be ready to provide sources if asked). In other words, answers here should be such as an historian of the subject would give. Not wikipedia. Not youtube videos.

Thank you.

Lot of it has to do with Hitler's book "Mein Kampf", where Hitler clearly stated that the eastern population of europe was subhumans, or atleast a sub race to the aryan. Hitler never wanted a war with the western countries, his goals was to colonize the east and the slavic population in the same way France and GB had colonized Africa, which was a colonial race Germany never was a part of. Germany at the time was a fascist regime, and the main enemy of fascists are communists.

That is what i've learned.

For what it's worth, Russia and the Soviet Union (which is what Nazi Germany attacked) are not the same thing. Russia was but one of several soviet republics that made up the Soviet Union (thus the union part in the Soviet Union). While Russia obviously dominated the political atmosphere in the USSR, it was actually the Ukraine and Belarus who primarily faced the brunt of the initial German invasion. Indeed when the Germans first invaded they played upon the nationalist sentiments of the non-Russian soviet citizens as a means of furthering the German war effort.

Info on the political structure of the USSR: http://en.wikipedia.org/wiki/Republics_of_the_Soviet_Union

Here is the start of a pretty interesting 10 part series that covers Stalin's premiership of the USSR; http://www.youtube.com/watch?v=G4hXhy8_hho.* It primarily focuses on WWII however and I believe part 3 talks about German's stirring up anti-Russian sentiments among western soviet republics.

*This series takes a fairly contemptuous view of Stalin. Obviously Stalin was a horrible person, be he wasn't quite the incompetent fool the series somewhat makes him to be. For example, a different take on why Stalin so mishandled the initial German invasion, wasn't because he couldn't believe Hitler would break the non-aggression pact/attack the USSR, but because he didn't want to be provoked into starting war he knew the USSR wasn't prepared for.