Lithuania, and the other Baltic States, fell victim to the Molotov-Ribbentrop pact. This agreement was signed between the USSR and Germany in August 1939; leading first to Lithuania being invaded by the Red Army on 15 June 1940, and then to its annexation and incorporation into the Soviet Union on 3 August 1940. The Soviet annexation resulted in mass terror, the denial of civil liberties, the destruction of the country's economic system and the suppression of Lithuanian culture. Between 1940 and 1941, thousands of Lithuanians were arrested and hundreds of political prisoners were arbitrarily executed. More than 17,000 people were deported to Siberia in June 1941. After the German attack on the Soviet Union, the incipient Soviet political apparatus was either destroyed or retreated eastward. Lithuania was then occupied by Nazi Germany for a little over three years. In 1944, the Soviet Union reoccupied Lithuania. Following World War II and the subsequent suppression of the Lithuanian Forest Brothers, the Soviet authorities executed thousands of resistance fighters and civilians whom they accused of aiding them. Some 300,000 Lithuanians were deported or sentenced to terms in prison camps on political grounds. It is estimated that Lithuania lost almost 780,000 citizens as a result of the Soviet occupation, of these around 440,000 were war refugees.