In late 1942 U.S. began its ground campaign against Germany with an invasion of North Africa. The German and Italian forces surrendered in May 1943, opening the way for the invasions of Sicily and Italy. Meanwhile, the U.S. Navy won a decisive victory over Japan in the Battle of Midway and began a campaign of island hopping in the Pacific. In 1943, the Allies launched an invasion of Italy and continued to pursue the island hopping strategy. The top Allied leaders met at the Tehran Conference in 1943, where they began to discuss post-war plans. Among the concepts discussed was the United Nations, an intergovernmental organization championed by Roosevelt that would replace the League of Nations after the war. In 1944, the U.S. launched a successful invasion of northern France and won a decisive naval victory over Japan in the Battle of Leyte Gulf. By the time of Roosevelt's death in April 1945, the U.S. had occupied portions of Germany and was in the process of capturing Okinawa. Germany and Japan surrendered in May-August 1945 during the administration of Roosevelt's successor Vice President Harry S. Truman.