The Soviet Union invaded eastern Poland on September 17, 1939, two and a half weeks after the Nazi German invasion of Poland of September 1. A two-pronged attack was decided in the secret Molotov-Ribbentrop Pact signed by the USSR with Germany in August 1939. As the bulk of the Polish Army had concentrated in the west of the country to fight the Germans, the Soviets met with limited resistance and their troops quickly moved westwards until they reached Brześć on September 22, where they met with the invading German army, and held the joint victory parade.