He attacked Russia in winter, that was his downfall. Besides, I'm not just talking strategist. The man gathered the pieces of what was a beaten and demoralised Germany and created one the most powerful military forces ever assembled. It took a coalition of world superpowers to end his campaign, and even then, his demise was more related on mistakes on his part than anything else. The man was a horrible human being, but lets not fool ourselves into thinking he was dumb, because he was anything but.