On September 17, the Red Army invaded eastern Poland and occupied the Polish territory assigned to it by the Molotov–Ribbentrop Pact, followed by co-ordination with German forces in Poland. Three Baltic States described by the Molotov–Ribbentrop Pact, Estonia, Latvia, and Lithuania, were given no choice but to sign a so-called "Pact of defense and mutual assistance" which permitted the Soviet Union to station troops in them.