Between September 3, 1939, when WWII began, and December 7, 1941, when Japan bombed Pearl Harbor, the United States gradually abandoned its policy of strict neutrality and moved to all-out war on the Allied side. The major events involved are outlined in the following sections.
        Events on this page are linked to both the historical timeline  and the diplomatic timeline  in order to set these developments in the full context of events in the rest of the world.

Cash and Carry

Shortly after war broke out in Europe, President Roosevelt asked Congress to repeal the arms embargo embodied in the Neutrality Act of 1937 so that arms could be sold to Britain and France.   In November, the Neutrality Act of 1939 was passed in order to   permit belligerents to purchase materials of war on a cash and carry basis.  However, while loosening U.S. isolationism in one respect, it banned American merchant ships from traveling in war zones, which constituted a strict municipal limitation on the traditional right of neutrals to free navigation of the seas.  Cash and Carry did aid Britain and France who, because their financial resources and control of the seas, were able to buy war materials in the United States as long as the goods never traveled on U.S. ships.  Though Cash and Carry marked a definite shift from pure isolation to pro-Allied neutrality, it actively sought to compensate for this by requiring that the U.S. relinquish some of its rights as neutrals.

Beginning of Active Aid to the Allies

The quick and unexpected fall of France to the Nazis in 1940   shocked most Americans out of their complacent attitude.  President Roosevelt determined that national security demanded that Germany not be permitted to become the dominate power in Europe and, along with the American public, became convinced tha the U.S. must privide the Allies with "all-out aid short of war."  Several significant developments in 1940 and 1941 indicated growing concern and increasing involvement.

• The Draft.   In September, 1940, after intensive debate, Congress adopted the first peacetime draft in American history.  The draft law made men between the ages of 21 and 35 liable for military service for one year.

• Re-election of Roosevelt in 1940.    During the campaign for the presidency in 1940, the national debate over neutrality reached its height.  Powerful isolationist groups, such as the American Fist Committee opposed any risks that could lead to war.  International groups called for more active aid to the Allies.  The nomination of internationalists for the Presidency by both major parties (Wendell Willkie (R) and Franklin D. Roosevelt (D)) was evidence of the national shift toward intervention. President Roosevelt viewed his re-election as a vote of support for a program of greater preparedness and aid to the Allies.

• The Destroyers for Bases Deal.    In September, 1940, President Roosevelt announced that, by executive agreement, the United States would exchange 50 overage destroyers for 99 year leases on British sea and air bases in the Western Hemisphere.  The Desrtoyers for Bases Deal is widely considered to have marked the functional death of U.S. neutrality and the beginning of a period of "non-beligerancy."

The Lend-Lease Act (March, 1941)  

By December, 1940, public opinion polls showed that 60% of the American people favored helping Britain even if it led to war.  In March, 1941, therefore, while Britain alone withstood the Nazi onslaught, the United States Congress passed the Lend-Lease Act.  The Lend-Lease Act empowered the president to "lend, lease, or exchange" war materials with nations whose struggle against aggression was considered necessary to American security.  It made the United States the "arsenal of democracy," and it became a factor in the final victory of the Allies.

Undeclared Naval War With Germany

The Lend-Lease Act led to a state of undeclared naval warfare with Germany. 

• In May, 1941, the United States established bases in Greenland and Iceland to help protect British and American convoys that were carrying goods and armaments to Britain (and later Russia). 
• In the same month, Germany announced that American naval assistance to Britain would bring retaliation.
• President Roosevelt quickly declared a state of unlimited emergency and announced that United States armed forces would be used to repel attack.  
• An American merchant ship, the Robin Moor, was torpedoed by a German submarine late in May, 1941.  During the summer and fall of 1941, German subs sank several more United States ships. American naval vessels and merchantmen counterattacked and began to destroy German submarines. 
• By December, 1941,  a state of undeclared naval war existed between the United States and Germany, and the United States was in effect an undeclared ally of Britain and Russia.