What nation signed a nonaggression pact with Germany?

Russia. He did this so he didn't have to worry about Russia when he invades Poland. The agreement is signed in August and he invades Poland in September just a few days after the agreement is signed. This was no mistake by Hitler, but planned by him. As soon as he invades the British react and declare war. He miscalculated the actions of what the British would do. Within a month Poland is divided up between Germany and Russia.