Britain entered the Pacific Ocean theater of World War II when Japan seized many British colonies in Asia in 1941–1942. After the Soviet Union and United States joined the Allies in 1941, the U.K. launched major offensives in North Africa, Italy, and Normandy. As a member of the Big Three, Prime Minister Winston Churchill participated in conferences with the US and USSR to plan the war and the postwar world; Britain became one of the Permanent members of the United Nations Security Council.