1. Napoleon’s main enemy was the British while Hitler’s was the Soviets so Napoleon’s invasion of Russia was a distraction while for Hitler the war with the Soviets was the entire part of the war in the first place.
Hitler literally had to invade Russia, Napoleon didn’t. They have similarities in the middle and end, but they’re fundamentally different in that first aspect.
Uh, Hitler and Stalin were allies up until Operation Barbarossa. Stalin was happy to have his own sphere of influence and probably wouldn't have bothered Hitler as long as he didn't threaten him. There was no reason for Nazi Germany and the USSR to fight except Hitler's anticommunism and his delusions of grandeur.
Anyway, the main differences between the two invasions is the nature of military technology, which, yes, made a prolonged campaign in Russia far more sustainable in 1941 than it was in 1812.
Both Hitler and Stalin understood that the Molotov-Ribbentrop pact was only a very temporary alliance and that armed confrontation between Germany and the USSR was inevitable at some point in the reasonably near future, but for Hitler to launch his attack in the summer of 1941 was ridiculously premature and a massive strategic own goal precipitated on ideology and paranoia, yeah. It’s absurd to say that he “had” to invade Russia at that point.
