'ABC-4' was the Allied agreement on overall strategy reached at the 'Arcadia' first conference in Washington (22 December 1941/14 January 1942).

This conference was the first inter-Allied meeting on military strategy between the British and US heads of government after the USA’s entry into World War II, and the major delegations were headed by Prime Minister Winston Churchill and President Franklin D. Roosevelt.

The 'Arcadia' conference also had a wider international diplomatic and political aspect concerning the terms of the post-war world, which followed from the Atlantic Charter agreed between Churchill and Roosevelt in August 1941. On 1 January 1942, 26 governments attending the conference agreed to the Declaration by United Nations. Although Roosevelt was under domestic pressure to concentrate the US war effort against Japan because of its 'Ai' attack on Pearl Harbor on 7 December, Germany’s declaration of war on the USA on 11 December made this decision more politically acceptable to opinion in the USA than it would otherwise have been.

With these developments, the US government agreed that the Allies' primary objective in winning the war was the defeat of Germany in the so-called 'Germany first' strategy. It was also agreed that the Allies' military resources against Germany and Italy would be combined under a single command in the European Theatre of Operations. The military agreements established that during 1942 the Allied powers would start to tighten the ring round Germany with blockade, aerial bombardment and secondary-theatre operations, specifically in the Mediterranean.