Why did Hitler want to attack Russia?

Hitler's main excuse for conquering the rest of Europe was a term he used: Lebensraum, which translates roughly "living space." He wanted to expand the available living space for the German people at the expense of all the other people living around them, especially to the east. He had laid all this out in his autobiographical book, Mein Kampf (My Struggle), had anyone besides dedicated Nazis bothered to read it. He was going to conquer the world. give it as a gift to the German people, and enslave, slaughter or starve the other peoples of the world for the benefit of the Germans.

Europe has always been crowded. Just look at the map. Germany in 1933, when Hitler came to power, had a population around 66 million people: this in a country of about 138,000 square miles, or about twice the size of the state of Wisconsin! That's around 478 people per square mile. For comparison, the population of Wisconsin in 2006 (I can't find the figure for 1933) was about 5.5 million, for a density of only 38 people per square mile - in our modern day! It doesn't take a mathematical genius to figure out why Hitler wanted to expand, or for that matter to figure out why so many Germans emigrated to Wisconsin in the 19th Century.

Of course, other European countries also had relatively large populations in relatively small land areas, but for Hitler and the Nazis that had no meaning whatsoever, since he was convinced that Germans were superior to all other humans and had a basic right to everyone else's property, land, and even lives. Hitler especially looked to the east, toward Czechoslovakia, Poland and especially the Soviet Union (Russia) where there was much less population density, and the people there were "only" Communists, Slavs, Jews and other "subhumans," according to Nazi ideology, so after Hitler conquered most of Western Europe in 1940, in 1941 he again attacked to the east, to gain Lebensraum in the lands under Soviet domination.

Before the war even started, Hitler bloodlessly annexed Austria in 1938 (Hitler was born in Austria but made no distinction between Austria and Germany and considered himself German). As soon as he did that he began agitating on behalf of the minority of ethnic Germans living in what was called the Sudetenland, at that time part of Czechoslovakia. In the so called Munich Accord, the Great Powers of Western Europe sacrificed the Czechs in what turned out to be a vain attempt to prevent another world war. Hitler was allowed to occupy the Sudetenland in 1938 and shortly thereafter the nation that had been Czechoslovakia ceased to exist. Even though ethnic Germans were only a quarter of the overall population, the Czechs and the Slovaks were driven out of the Sudetenland and the area became exclusively German.

After 1795 Poland had also ceased to exist and had been divided among Russia, Prussia, and Austria. Prior to 1918 the western part of what had been Poland was part of the German Empire (Reich) and only regained its independence after the German defeat in World War 1. So far as Hitler was concerned, Western Poland still belonged to Germany, and as soon as he invaded in 1939 the Nazis began killing Poles, Polish Jews, and moving whole populations eastward to make room for ethnic Germans to come in and take over lands that had been forcibly vacated by the German conquest. (It must not be forgotten that under the terms of the nonaggression pact the Nazis had signed with the Soviets just days before Hitler invaded, Stalin came in and did the same thing in the eastern half of Poland.)

Had Hitler been successful in conquering the then Soviet Union in 1941 or 1942, there would have been no one left to fight him except Britain and the U.S., and World War 2 might have had a different outcome.