Why did Germany sign a non-aggression pact with the Soviet Union in 1939

Germany and the Soviet Union signed the non aggression act as to promise not to attack each other and allowing Germany to attack poland on september 1st 1939.

since the SU was on the brink of another major war Stalin found it would be important to have peaceful terms with Germany. The SU needed time to build up their army and Adolf Hitler needed assurance that Germany would attack Poland. In which was the beginning of their plans to divide Eastern Europe.