United States

Although in retrospect U.S. entry into World War II seems inevitable, in 1941 it was still the subject of great debate. Isolationism was a great political force, and many influential individuals were determined that U.S. aid policy stop short of war. In fact, as late as August 12, 1941, the House of Representatives extended the Selective Training and Service Act of 1940 by a vote of only 203 to 202. Despite isolationist resistance, Roosevelt pushed cautiously forward. In late August the navy added British and Allied ships to its Icelandic convoys. Its orders were to shoot German and Italian warships on sight, thus making the United States an undeclared participant in the Battle of the Atlantic. During October one U.S. destroyer was damaged by a German U-boat and another was sunk. The United States now embarked on an undeclared naval war against Germany, but Roosevelt refrained from asking for a formal declaration of war. According to public opinion polls, a majority of Americans still hoped to remain neutral.

The war question was soon resolved by events in the Pacific. As much as a distant neutral could, the United States had been supporting China in its war against Japan, yet it continued to sell Japan products and commodities essential to the Japanese war effort. Then, in July 1940, the United States applied an embargo on the sale of aviation gas, lubricants, and prime scrap metal to Japan. When Japanese armies invaded French Indochina in September with the apparent purpose of establishing bases for an attack on the East Indies, the United States struck back by embargoing all types of scrap iron and steel and by extending a loan to China. Japan promptly retaliated by signing a limited treaty of alliance, the Tripartite Pact, with Germany and Italy. Roosevelt extended a much larger loan to China and in December embargoed iron ore, pig iron, and a variety of other products.

Japan and the United States then entered into complex negotiations in the spring of 1941. Neither country would compromise on the China question, however, Japan refusing to withdraw and the United States insisting upon it. Believing that Japan intended to attack the East Indies, the United States stopped exporting oil to Japan at the end of the summer. In effect an ultimatum, since Japan had limited oil stocks and no alternative source of supply, the oil embargo confirmed Japan’s decision to eliminate the U.S. Pacific Fleet and to conquer Southeast Asia, thereby becoming self-sufficient in crude oil and other vital resources. By the end of November Roosevelt and his military advisers knew (through intercepted Japanese messages) that a military attack was likely; they expected it to be against the East Indies or the Philippines. To their astonishment, on December 7 Japan directed its first blow against naval and air installations in Hawaii. In a bold surprise attack, Japanese aircraft destroyed or damaged 18 ships of war at Pearl Harbor, including the entire battleship force, and 347 planes. Total U.S. casualties amounted to 2,403 dead and 1,178 wounded.

Pearl Harbor, HawaiiFord Island in Pearl Harbor, Hawaii, as seen from a Japanese aircraft during the attack on the U.S. Pacific Fleet, December 7, 1941.National Archives, Washington, D.C.

On December 8, 1941, Congress with only one dissenting vote declared war against Japan. Three days later Germany and Italy declared war against the United States; and Congress, voting unanimously, reciprocated. As a result of the attack on Pearl Harbor, the previously divided nation entered into the global struggle with virtual unanimity.

The United States at war

Although isolationism died at Pearl Harbor, its legacy of unpreparedness lived on. Anticipating war, Roosevelt and his advisers had been able to develop and execute some plans for military expansion, but public opinion prohibited large-scale appropriations for armament and defense. Thus, when Pearl Harbor was attacked, the United States had some 2,200,000 men under arms, but most were ill-trained and poorly equipped. Barely a handful of army divisions even approached a state of readiness. The Army Air Corps possessed only 1,100 combat planes, many of which were outdated. The navy was better prepared, but it was too small to fight a two-ocean war and had barely been able to provide enough ships for convoy duty in the North Atlantic. Eventually more than 15,000,000 men and women would serve in the armed forces, but not until 1943 would the United States be strong enough to undertake large-scale offensive operations. (For U.S. military involvement in World War II, see the article World War II.)

War production