Hitler had only two chances of winning the war (or at least not losing it). Defeat or make peace with Great Britain in the summer of 1940 or give a fatal blow to the USSR in the summer of 1941. He failed on both. Other decisions, like going for the Med in 1941, not declaring war to the USA or making earlier his wonder weapons could have helped him, but not decisively in my opinion. Invading Britain was imposible in face of the Royal Navy, but who knows if an effective blockade, or the taking of Egypt could have forced peace. In the USSR, his only real chance was taking Moscow in august, and the area behind the city up to Gorki and Tuzla. This was the core of the USSR, had a lot of important industries, the greatest centers of slavic (id est, more reliable) population to recruit, and the communications hub. Maybe it would have not been decisive, but it was german's best chance, as a lot of commander saw it.