The millions of troops he sent eastward to Russia would have easily destroyed the allies as a fighting force in Africa, probably knocking Britain out of the fighting. Churchill said as much to Roosevelt. That is how important the often underplayed African campaign was to the overall war effort.
Hitler's obsession with Russia, which cost him millions of troops and weaponry, was a fatal flaw which enabled the allies to prevail in Africa and defeat the Axis Powers' hopes of ultimate victory in Europe.
Hitler didn't have much of a choice, he had to attack Russia before Russia became powerful enough to launch an offensive strike of their own, which would have probably happened by 1943. That's why Stalin tried not to provoke Hitler until then, even when he suspected the Nazis would strike in 1941.