[2] It was a secret clause as amended on 28 September 1939 by Nazi Germany and the Soviet Union after their joint invasion and occupation of sovereign Poland.

[3] It was signed by Joachim von Ribbentrop and Vyacheslav Molotov, the foreign ministers of Germany and the Soviet Union respectively, in the presence of Joseph Stalin.

Only a small portion of the protocol, which superseded the first treaty, was publicly announced, while the spheres of influence of Nazi Germany and the Soviet Union remained secret.

The third secret protocol of the Pact was signed on 10 January 1941 by Friedrich Werner von Schulenburg and Molotov, in which Germany renounced its claims on a part of Lithuania, west of the Šešupė river.

The mutual assistance treaties allowed for the 1940 Soviet occupation of the Baltic states and was described by The New York Times as "virtual sacrifice of independence".