Diplomacy of the Second World War

Warnings, Guarantees, and the Opening of War

Japan was already fighting a major war in China when Germany invaded Poland on 1 September 1939. In Europe, Britain and France had promised support to Poland after German expansion destroyed confidence in further concessions to Hitler. In Asia, American opposition to Japan’s conquests increasingly took the form of aid to China and restrictions on trade with Japan. The disputes concerned territory, imperial power, and the willingness of governments to defend increasingly costly prior commitments. [1] [2]

After Germany invaded Poland, London exchanged telegrams with Berlin, Paris, Warsaw, and Rome while officials considered warnings and possible mediation. On 3 September, British ambassador Nevile Henderson carried the final demand to Berlin: unless assurances ending German aggression reached London by 11 a.m., a state of war would exist. No acceptable answer arrived. [1]

When Negotiation and Attack Overlapped

In Washington, Japanese ambassador Kichisaburō Nomura and special envoy Saburō Kurusu continued discussions with Secretary of State Cordell Hull during the crisis of 1941. On 7 December they delivered Tokyo’s final message after the attack on Pearl Harbor had begun. Nomura said he had been instructed to deliver it at 1 p.m. Washington time but that decoding had delayed him; Hull received the envoys at 2:20. Their exchange failed to warn the United States of the operational attack. [3]

After Germany invaded the Soviet Union in June 1941, Washington and Moscow began military cooperation. Roosevelt sent Harry Hopkins to Moscow to discuss Soviet needs, and American supplies followed. The Soviet Union pressed its allies for an earlier invasion of western Europe, while British and American leaders argued over military feasibility. The Atlantic Charter set out common Anglo-American war aims. [4] [5]

Tehran and Yalta

At Tehran in late 1943, Roosevelt, Churchill, and Stalin agreed on plans for the invasion of France. Soviet operations would help prevent Germany from concentrating forces against the landing. The Normandy landings followed in June 1944, after years of dispute about where and when the Western Allies would attack. [6]

By Yalta in February 1945, military victory appeared closer, but control of liberated and defeated territory raised new disputes. The leaders addressed occupation of Germany, elections in Europe, Soviet entry into the war against Japan, and the rules of the proposed United Nations. [7]

Surrender and Occupation

In August 1945, after atomic attacks and Soviet entry into the war against Japan, Japan sent its acceptance of the Potsdam terms with a reservation about the emperor’s position. With diplomatic relations severed, Secretary of State James Byrnes asked the Swiss chargé on 11 August to transmit the Allied response: the emperor and Japanese government would be subject to the Supreme Commander of the Allied Powers. [4] [8]

The instrument signed in Tokyo Bay on 2 September directed Japanese forces to surrender and civil and military officials to obey Allied orders. It named the Republic of China among the Allied powers, alongside the United States, Britain, and the Soviet Union. Ending combat required more than announcing defeat: instructions had to reach scattered commands, prisoners had to be released, and an occupation authority had to be recognized. These arrangements opened a new period in which former enemies would negotiate peace treaties and the restoration of diplomatic relations. [9]

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