The line became a major geopolitical factor during World War II, when the USSR invaded eastern Poland, resulting in the split of Poland's territory between the USSR and Nazi Germany along the Curzon Line. After the German attack on the Soviet Union in 1941, Operation Barbarossa, the Allies did not agree that Poland's future eastern border should be kept as drawn in 1939 until the Tehran Conference. Churchill's position changed after the Soviet victory at the Battle of Kursk.