Yalta, Casablanca, Potsdam The most important meetings of the Second World War were held between the United Kingdom, the Union of Soviet Socialist Republics and the United States of America. The most important gatherings of the rulers of these countries were at Casablanca, in 1943, at Yalta, in 1945, and at Potsdam, in 1945. During these meetings, Winston Churchill, representing the UK, Iosif Stalin, representing the USSR, Franklin Roosevelt and later Harry Truman, representing the US, ...