Allies of World War II

Overview

The Allies of World War II were the coalition that opposed and defeated the Axis powers — the “Big Four” of the United Kingdom, the Soviet Union, the United States, and China, plus France while it was unoccupied, and every other signatory of the Declaration by United Nations of 1 January 1942 (Encyclopaedia Britannica). After the war the alliance, and the Declaration that bound it, “would become the basis of the modern United Nations” (Encyclopaedia Britannica; The National WWII Museum).

The alliance’s oddest fact is its beginning. “Unlike the Axis, the Allies were not united by a treaty before the war” — the coalition assembled itself member by member, as each was attacked (The National WWII Museum). For over a year it was barely a coalition at all: from mid-1940 to mid-1941, after France surrendered and before the Soviet Union and the United States entered, “the United Kingdom and its former colonies were effectively the only Allies in action” (Encyclopaedia Britannica).

Assembled by aggression

The Allies began as a pledge: Britain and France promised to aid Poland if Germany invaded. When Germany attacked on 1 September 1939, both declared war on 3 September; the independent British dominions — Australia, Canada, New Zealand, South Africa — followed within days (Encyclopaedia Britannica). Then came the occupations that briefly widened the alliance and then shrank it: Denmark and Norway on 9 April 1940, the Low Countries that May, Greece on 28 October 1940, Yugoslavia on 6 April 1941 — each quickly conquered, each contributing a government-in-exile (Encyclopaedia Britannica; The National WWII Museum). Figures like France’s Charles de Gaulle fled abroad, refused surrender, and led resistance from the outside (The National WWII Museum).

On 22 June 1941 came what Britannica calls an “unexpected gift”: Germany’s invasion of the Soviet Union, producing an Anglo-Soviet treaty on 12 July (Encyclopaedia Britannica). The ideologically opposed Adolf Hitler and Joseph Stalin had held a short-term nonaggression bargain; Hitler’s betrayal “brought Stalin into the war on the British side” (The National WWII Museum). With American lend-lease support, the Soviet Union “became a nightmare for the German military,” pushing it all the way back to Berlin (Encyclopaedia Britannica).

The United States supplied arms but stayed neutral until the attack on Pearl Harbor on 7 December 1941 — and then, “for reasons still debated today,” Germany declared war on the United States on 11 December, bringing America “fully into the Allied fold” (Encyclopaedia Britannica). Before that, Franklin Roosevelt had conducted secret diplomacy with Churchill — the two met in August 1941 and issued the Atlantic Charter, a statement of postwar goals that “was not a formal alliance” (The National WWII Museum). A nice footnote: Bulgaria, Hungary, and Romania declared war on America in December 1941, but the United States did not declare war in return until June 1942 (The National WWII Museum).

The formal alliance and how it fought

On 1 January 1942, during the Arcadia Conference in Washington, Roosevelt and Churchill proclaimed the Declaration by United Nations: 26 original signers — the US, Britain, the USSR, and China; the British dominions; Latin American states; European governments-in-exile — with 21 more, including France, joining before the war’s end (The National WWII Museum). The three wartime leaders — Roosevelt, Churchill, Stalin — became the “Big Three” (The National WWII Museum).

The Allies built the coordination machinery the Axis never did: Roosevelt and Churchill established the Combined Chiefs of Staff to run Anglo-American military cooperation (Encyclopaedia Britannica). Their strategy was hashed out in five summit conferences: Arcadia (December 1941, the “Europe first” strategy), Casablanca (January 1943, the Sicily invasion plan and the unconditional-surrender demand), Tehrān (November 1943, the second front in Western Europe), Yalta (February 1945, the defeat and occupation of Germany and the fate of eastern Europe), and Potsdam (July 1945, the administration of defeated Germany and Poland’s boundaries) (Encyclopaedia Britannica).

The material basis of victory was American industry. The United States, which Roosevelt called “an arsenal of democracy,” had a production capacity that “dwarfed that of any other country” — by war’s end it produced almost two-thirds of all the Allies’ military equipment, and mobilized more than 16 million people, more than any Allied power except the Soviet Union (Encyclopaedia Britannica). The Normandy landings of 6 June 1944 opened the second front; the Red Army converged from the east; Hitler killed himself on 30 April 1945 and Germany surrendered on 8 May (Encyclopaedia Britannica). In the Pacific, the “island hopping” campaign and the atomic bombings of Hiroshima and Nagasaki forced Japan to surrender, formally on 2 September 1945 (Encyclopaedia Britannica).

The alliance ended the war with 47 member states — some previously neutral countries, like Saudi Arabia, joined only because siding against the Axis was made a precondition for attending the founding UN conference — and all 47 became charter members of the United Nations when its charter was signed on 26 June 1945 (Encyclopaedia Britannica).

Frequently asked questions

Who were the main Allied powers?

The “Big Four” — the United Kingdom, the Soviet Union, the United States, and China — with France while it was unoccupied; the wartime leaders Roosevelt, Churchill, and Stalin were the “Big Three” (Encyclopaedia Britannica; The National WWII Museum).

How did the Allies become a formal alliance?

Through the Declaration by United Nations, proclaimed 1 January 1942 during the Arcadia Conference, with 26 original signers (The National WWII Museum).

How did the Axis become the Allies’ problem?

Britain and France declared war after the 1939 invasion of Poland; the USSR joined after Germany invaded it in June 1941; the US joined after Pearl Harbor and Germany’s 11 December 1941 declaration of war on America (Encyclopaedia Britannica).

What did the Allies become?

The United Nations: the 47 Allied member states at war’s end all became charter members of the UN (Encyclopaedia Britannica; The National WWII Museum).

What this profile does not claim

This profile follows Britannica’s membership accounting and does not fix accession dates for every one of the 47 member states. It does not offer a theory for why Germany declared war on the United States on 11 December 1941 — Britannica says the reasons are “still debated today.” It does not adjudicate the Allied internal disagreements (the second-front timing, the fate of eastern Europe) beyond what the sources report, and it treats the wartime “United Nations” name as the historical usage, distinct from the post-1945 permanent organization.