Diplomatic history of World War II

The diplomatic history of World War II includes the major foreign policies and interactions inside the opposing coalitions, the Allies of World War II and the Axis powers, between 1939 and 1945.

High-level diplomacy began as soon as the war started in 1939. British Prime Minister Winston Churchill^[1] forged close ties with France and sought close ties with the United States, especially through his relationship with President Franklin Roosevelt. When the Soviet Union joined the war in June 1941, the Grand Alliance expanded to a three-way relationship among Churchill, Roosevelt, and Joseph Stalin of the Soviet Union. American diplomacy stepped up after it entered the war in December 1941 and was bolstered by large quantities of financial and economic assistance, especially after the Lend-Lease programme began to attain full strength during 1943. The Soviet Union's main diplomatic goal at first was to win support to defend against the massive German invasion. With victory in sight by 1944, Moscow began creating satellite states, first of all in Poland and East Germany. The main British goals were to defeat the German threat, maintain British roles in Central and Eastern Europe, and preserve the British Empire. The British dominions and India contributed significantly to warfighting but did not have a voice in major Allied decisions. Roosevelt was hostile to the idea of the British, French, and other empires, but was forced by Churchill to postpone interference in India. Roosevelt's main goal by 1943 was the creation of a postwar United Nations, controlled by the Big Three, with major roles also for China and France. However, China and France had only small roles in wartime diplomacy. Roosevelt was increasingly troubled by Moscow's aggressive intentions late in the war but decided that with the United Nations in place, and his own persuasive personal relationship with Stalin, problems could be resolved after the war.

For the Axis powers diplomacy was a minor factor. The alliance of Germany, Italy, and Japan was always informal, with minimal assistance or coordination. Hitler had full control of German diplomatic policies and imposed his will on his allies in Eastern Europe, and with the puppet regime in northern Italy after 1943. Japan's diplomats had a minor role in the war, as the military was in full control. A dramatic failure was the inability of Tokyo to obtain the formulas for synthetic oil from Germany until it was too late to overcome the fatal shortage of fuel for the Japanese war machine. Practically all the neutral countries broke with Germany before the end of the war and thereby were enabled to join the new United Nations.

The military history of the war is covered at World War II. The prewar diplomacy is covered in Causes of World War II and International relations (1919–1939). After the war, diplomacy revolved around the Cold War.