The correct answer is - Soviet Union.
Germany, under Adolf Hitler, managed to strike an agreement with the Soviet Union, under Joseph Stalin, so that the countries do not attack each other, and that they will stay out of each other's way of their interest zones.
The deal basically was made so that the two countries do not enter a mutual conflict, weaken from it, and than be taken down by the allies. Stalin was very happy with the deal, and was somehow sure that Hitler is honest, until the German leader decided that his interest is in the Soviet Union as well and attacked it.