On February 24, 1918, Estonia is declared a democratic and independent republic. On February 2, 1920, the Treaty of Peace between RSFSR and the Republic of Estonia was signed in Tartu, where both parties offi cially recognized reciprocally. During 1920-1939, relations between Estonia and the Soviet Union were governed by the treaty system signed by the two countries. The non-aggression treaty between Estonia and the USSR, signed on May 4, 1932, stipulated that the contracting parties had to ensure the inviolability of the common border and to refrain from any reciprocal attack and from any kind of violence directed against territorial integrity and political independence of the other Contracting Party. Relations between the two countries changed dramatically after the Molotov-Ribbentrop Pact was signed on August 23, 1939. On September 28, 1939, the Estonian Republic was forced to sign an agreement to ensure the permanent presence of 25,000 Soviet soldiers on Estonian territory, and on June 17, 1940, following the Soviet ultimatum, the Red Army troops occupied Estonia.