In September, 1939 the Soviet Union occupied the eastern voivodeships of Poland. During World War II, the occupied territory was annexed and ceded to the Soviet republic of: Ukrainian SSR, Byelorussian SSR and the Lithuanian Soviet Socialist Republic. The annexation of this part of Poland was accepted at the Tehran and Yalta Conference. As a result, under the pressure of world powers, Poland was forced to cede the Soviet Union 48% of its territory, equating to the loss of 178,000 km² of land, gaining the equivalent of 101 000 km² in the west. The modification of Poland's borders by the United Kingdom and the United States of America was a direct violation of the Atlantic Charter.