Well, the nazi party would only be a radical right wing political party, if it ever managed to get off the ground. I doubt it would, but anyway the Weimer Republic would survive. Gustav Stresemann would most likely be reelected as Chancellor term after term, with his most direct problem being communism after solving the inflation problems.
The Second World War would most likely be the result of Stalin's ambitions as a dictator. He would attack the Low Countries and Germany, who would defend themselves for all they were worth before calling for help from France and Britain.
I do not believe the allies would help Germany until they realized that the German and Low Country forces will eventually fail. And with a communist Germany, France itself would be affected.
And so I will conclude this by saying that after one or two years of warfare the allies would be formed (excluding the United States who I believe would be fighting Japan and Japan alone) and the Russians would be beaten back.
But unless they would be able to capture Moscow and Petrograd during the summer (or spring) and avoid the winter, I believe a stalemate would occur. With the allies fearing the Russian winter and the Russians being unable to invade Europe.