The treaty of non-agretion between Germany and the Union of Soviet Sociacist Republics also called as the Molotov-Ribbentrop Pact was a neutrally pact between the Nazi Germany and the Soviet Union signed in August of 1939.
The clauses provided a written guarantee of non-beligerance by each party towards the other and a commitment of no alliance with an enemy of the ohter party. In addition the treaty contained a secret protocol in which they defined the borders of the so called "spheres of influence" in the possible events of an invasion to Poland, Lithuania, Latvia, Estonia and Finland.
After the signature of the pact Germany and the Soviet Union invaded Poland with a few days of distance between both operations and the new borders was set up by the secret protocol.
The secret protocol was just a rumour untill it was made public at the Nuremberg Trials.
I hope this answer have helped you. Regards.
