During the Second World War British Prime Minister Winston Churchill's friendship with the U.S.A. President Franklin D. Roosevelt was Great Britain’s lifeline.

Britain had lost most of her army equipment during the evacuation from Dunkirk. This was the first defeat for the British under Churchill. To make matters worse Britain’s funds were almost exhausted and most of her overseas interests had been sold to pay for the war effort.

According to international law, weapons could not be sold to warring countries and other goods could only be exported on a cash-down basis. Because Britain had almost no funds at all Churchill appealed to Roosevelt to help him find some other form of payment.

President Roosevelt was determined to keep the U.S.A. out of the war but was also determined to help Britain and persuade the American people that it was in the U.S.A.’s best interest to help nations opposed to the Nazis.

In the Lease-lend Agreement of 1941, Roosevelt persuaded the U.S. Congress to let Britain have weapons and other military equipment and to allow Britain to pay for this after the war. Without this (weapons, aircraft, food and petrol) Britain may not have been able to stand up to Nazi Germany during the first few months of 1941.

Japan's attack on Pearl Harbour in December 1941 brought the United States into the war, and Hitler declared war on the United States. The U.S.A. and Great Britain became allies and Churchill and Roosevelt continued to work together during the war. The first results of allied co-operation were the landings in North Africa, the following German defeat there and the invasion of Sicily and Italy. But it was not until the summer of 1944 that preparations were complete for the Allied invasion of France (D-day) to break open Hitler's Europe.

Churchill and Roosevelt set out their war aims in the Atlantic Charter, signed in August 1941 and continued to work together closely until the last year of the war when the famous partnership started to dissolve. The two did not agree on containing Soviet expansion after the war.