FDR: Foreign policy 1933-41 :: The rejection of the League of Nations treaty in 1919 marked the dominance of isolationism in American foreign policy ... The rise to power of Adolf Hitler in Germany aroused fears of a new world war. In 1935, at the time of Fascist Italy's invasion of Abyssinia, Congress passed the Neutrality Act, applying a mandatory ban on the shipment of arms from the U.S. to any combatant nation. Roosevelt opposed the act on the grounds that it penalized the victims of aggression such as Abyssinia, and that it restricted his right as President to assist friendly countries, but he eventually signed it. In 1937 Congress passed an even more stringent Act, but when the Sino-Japanese War broke out in 1937 Roosevelt found various ways to assist China, and warned that Fascist Italy, Nazi Germany and Imperial Japan were threats to world peace and to the U.S. When World War II in Europe broke out in 1939, Roosevelt became increasingly eager to assist Britain and France, and he began a regular secret correspondence with Winston Churchill, in which the two freely discussed ways of circumventing the Neutrality Acts. In May 1940 Germany attacked France and rapidly occupied the country, leaving Britain vulnerable to German air attack and possible invasion. Roosevelt was determined to prevent this and sought to shift public opinion in favor of aiding Britain.
FDR: The path to war :: The most pressing issue was the urgent necessity of assisting Britain, whose financial resources were exhausted by the end of 1940. Congress, where isolationist sentiment was in retreat, passed the Lend-Lease Act in March 1941, allowing Britain to "lease" huge amounts of military equipment on the basis of a promise that they would be paid for after the war. Britain was also forced to agree to dismantle preferential trade arrangements that kept American exports out of the British Empire. This underlined the point that the war aims of the U.S. and Britain were not the same. Roosevelt was a lifelong free trader and anti-imperialist, and ending European colonialism was one of his objectives. This did not prevent the forming of a close personal relationship with Churchill, who became British Prime Minister in May 1940. When Germany invaded the Soviet Union in June 1941, Roosevelt extended Lend-Lease to the Soviets. During 1941 Roosevelt also agreed that the U.S. Navy would escort Allied convoys as far east as Iceland, and would fire on German ships or submarines if they attacked Allied shipping within the U.S. Navy zone. Thus by mid-1941 Roosevelt had committed the U.S. to the Allied side with a policy of "all aid short of war."
FDR: Pearl Harbor :: Roosevelt was less keen to involve the U.S. in the war developing in East Asia, where Japan occupied French Indo-China in late 1940. He authorized increased aid to China, and in July 1941 he restricted the sales of oil and other strategic materials to Japan, but also continued negotiations with the Japanese government in the hope of averting war. Through 1941 the Japanese planned their attack on the western powers, including the U.S., while spinning out the negotiations in Washington. The "hawks" in the Administration, led by Stimson and Treasury Secretary Henry Morgenthau, were in favor of a tough policy towards Japan, but Roosevelt, emotionally committed to the war in Europe, refused to believe that Japan might attack the U.S. and favored continued negotiations. The U.S. Ambassador in Tokyo, Joseph C. Grew, passed on warnings about the planned attack on the American Pacific Fleet's base at Pearl Harbor in Hawaii, but these were ignored by the State Department. On 7 December 1941 the Japanese attacked the U.S. fleet at Pearl Harbor, damaging most of it and killing 3,000 American personnel. The American commanders at Pearl Harbor, Admiral Husband E. Kimmel and General Walter Short, were taken completely by surprise, and were later made scapegoats for this disaster. The fault really lay with the War Department in Washington, who since August 1940 had been able to read the Japanese diplomatic codes and had thus been given ample warning of the imminence of the attack (though not of its actual date). In later investigations, the War Department claimed that it had not passed warnings on to the commanders in Hawaii because its analysts refused to believe that the Japanese would really have the effrontery to attack the United States.