During the summer and autumn of 1941, German troops advanced deep into the Soviet Union, but stiffening Red Army resistance prevented the Germans from capturing the key cities of Leningrad and Moscow. On December 6, 1941, Soviet troops launched a significant counteroffensive that drove German forces permanently from the outskirts of Moscow. One day later, on December 7, 1941, Japan (one of the Axis powers) bombed Pearl Harbor, Hawaii. The United States immediately declared war on Japan. On December 11, Germany and Italy declared war on the United States as the military conflict widened.