On 16 December 1944, Germany made a last attempt on the Western Front by using most of its remaining reserves to launch a massive counter-offensive in the Ardennes and along the French-German border to split the Western Allies, encircle large portions of Western Allied troops and capture their primary supply port at Antwerp to prompt a political settlement. By January, the offensive had been repulsed with no strategic objectives fulfilled. In Italy, the Western Allies remained stalemated at the German defensive line. In mid-January 1945, the Soviets and Poles attacked in Poland, pushing from the Vistula to the Oder river in Germany, and overran East Prussia. On 4 February, Soviet, British and US leaders met for the Yalta Conference. They agreed on the occupation of post-war Germany, and on when the Soviet Union would join the war against Japan. In February, the Soviets entered Silesia and Pomerania, while Western Allies entered western Germany and closed to the Rhine river. By March, the Western Allies crossed the Rhine north and south of the Ruhr, encircling the German Army Group B, while the Soviets advanced to Vienna. In early April, the Western Allies finally pushed forward in Italy and swept across western Germany capturing Hamburg and Nuremberg, while Soviet and Polish forces stormed Berlin in late April. American and Soviet forces met at the Elbe river on 25 April. On 30 April 1945, the Reichstag was captured, signalling the military defeat of Nazi Germany. Several changes in leadership occurred during this period. On 12 April, President Roosevelt died and was succeeded by Harry S. Truman. Benito Mussolini was killed by Italian partisans on 28 April. Two days later, Hitler committed suicide, and was succeeded by Grand Admiral Karl Dönitz.. Leaders from which nationals met for the Yalta Conference and on what date?