On 23 August 1939 the
Soviet Union asserted its control over the Baltic states with the
Molotov–Ribbentrop Pact. The Soviets
invaded Poland on 17 September, concluding operations on 6 October. After occupying eastern
Poland, the Soviets pressured
Finland and the Baltic states to conclude mutual assistance treaties. The Soviets questioned the neutrality of
Estonia following the
escape of a Polish submarine on 18 September. A week later, on 24 September, the Estonian foreign minister
Karl Selter was given an ultimatum in Moscow. After four days of negotiations, the Estonians had no choice but to accept naval, air and army bases. Soviet troop numbers in Estonia were put at 25,000. The
mutual assistance treaty was signed on 28 September. As a result, soon two other Baltic states yielded to Soviet pressure. ==Articles of the treaty==