President Franklin Roosevelt quickly decided that America could not fight major campaigns in the Pacific and in Europe at the same time. He and his advisors decided to fight first against the Germans and Italians. Then, when victory in Europe seemed sure, the United States could turn to fight the Japanese in Asia.
This left the Japanese free to extend their power throughout Asia and the western Pacific. Soon after the attack at Hawaii, Japanese forces invaded Hong Kong, Malaya, and the Philippines. American land and air forces in the Philippines were destroyed or captured. And Manila fell to Japanese troops. In February, 1942, Japan's forces won a great victory against the British in Singapore.
Japanese forces marched into Burma. They attacked Ceylon and captured the Andaman Islands in the Bay of Bengal. The Japanese military forces seemed too strong to stop.
President Roosevelt sent some forces to the Pacific. And he began to re-build the American naval forces destroyed at Pearl Harbor. But he sent most of America's military strength to Europe. The United States rushed troops and war equipment to help Britain survive against Hitler's Germany.
American military leaders wanted to fight Germany quickly by launching an attack across the English Channel. But British Prime Minister Winston Churchill opposed this.
He and others feared such an invasion might fail. So, British and American forces attacked Italian and German occupation troops in North Africa. They defeated them, then crossed the Mediterranean Sea to attack enemy forces in Sicily. Within weeks, they pushed the Germans out of Sicily to the Italian mainland. The Allied invasion of Italy followed.
Hitler could not strengthen his forces in North Africa and Italy, because Germany also was fighting hard in the Soviet Union.
Hitler's decision early in the war to attack the Soviet Union was a serious mistake. It divided his men and materials. His plan was to defeat Soviet forces quickly with one strong attack. But he failed. And his failure cost him valuable troops and supplies that might have helped him win the battles for North Africa and Italy.