The SyriaLebanon campaign, also known as Operation Exporter, was the British invasion of Vichy French Syria and Lebanon from JuneJuly 1941, during the Second World War. The French had ceded autonomy to Syria in September 1936, with the right to maintain armed forces and two airfields in the territory.

On 1 April 1941, the 1941 Iraqi coup d'tat had taken place and Iraq had come under the control of Iraqi nationalists led by Rashid Ali, who appealed for Italian and German support. The Anglo-Iraqi War (231 May 1941) led to the overthrow of the Ali regime and the installation of a pro-British government. During this conflict, key Vichy figure Admiral Franois Darlan had allowed German aircraft to use Vichy airfields in Syria for attacks against the British in Iraq. The British invaded Syria and Lebanon in June, to prevent Nazi Germany from using the Vichy French-controlled Syrian Republic and French Lebanon as bases for attacks on Egypt, during an invasion scare in the aftermath of the German victories in the Battle of Greece (630 April 1941) and the Battle of Crete (20 May 1 June). In the Western Desert Campaign (19401943) in North Africa, the British were preparing Operation Battleaxe to relieve the siege of Tobruk and were fighting the East African Campaign (10 June 1940 27 November 1941) in Ethiopia and Eritrea.

The Vichy French conducted a vigorous defence of Syria but, on 10 July, as the 21st Australian Brigade was on the verge of entering Beirut, the French sought an armistice. At one minute past midnight on 12 July, a ceasefire came into effect and ended the campaign. The Armistice of Saint Jean d'Acre (Convention of Acre) was signed on 14 July at the Sidney Smith Barracks on the outskirts of the city. While it was taking place, Time magazine referred to the fighting as a "mixed show", and the campaign remains little known, even in the countries that took part. There is some evidence that the British censored reportage of the fighting because politicians believed that even highly-necessary hostilities against French forces could have a negative effect on public opinion in English-speaking countries.

The Allies, later known formally as the United Nations, were an international military coalition formed during the Second World War (1939–1945) to oppose the Axis powers, led by Nazi Germany, Imperial Japan, and Fascist Italy. Its principal members by 1941 were the United Kingdom, United States, Soviet Union, and China.

Membership in the Allies varied during the course of the war. When the conflict broke out on 1 September 1939, the Allied coalition consisted of the United Kingdom, France, and Poland, as well as their respective dependencies, such as British India. They were soon joined by the independent dominions of the British Commonwealth: Canada, Australia, New Zealand and South Africa. Consequently, the initial alliance largely resembled that of the First World War.

As Axis forces began invading northern Europe and the Balkans, the Allies added the Netherlands, Belgium, Norway, Greece, and Yugoslavia. The Soviet Union, which initially had a nonaggression pact with Germany and participated in its invasion of Poland, joined the Allies in June 1941 after Operation Barbarossa. The United States, while providing some materiel support to European Allies since September 1940, remained formally neutral until the Japanese bombing of Pearl Harbor in December 1941, after which it declared war and officially joined the Allies. China had already been at war with Japan since 1937, but formally joined the Allies in December 1941.

The Allies were led by the so-called "Big Three"—the United Kingdom, the Soviet Union, and the United States—which were the principal contributors of manpower, resources, and strategy, each playing a key role in achieving victory. A series of conferences between Allied leaders, diplomats, and military officials gradually shaped the makeup of the alliance, the direction of the war, and ultimately the postwar international order. Relations between the United Kingdom and the United States were especially close, with their bilateral Atlantic Charter forming the groundwork of the alliance.

The Allies became a formalized group upon the Declaration by United Nations on 1 January 1942, which was signed by 26 nations around the world; these ranged from small nations far removed from the war, to governments in exile from the Axis occupation. The Declaration officially recognized the Big Three and China as the "Four Powers", acknowledging their central role in prosecuting the war; they were also referred to as the "trusteeship of the powerful", and later as the "Four Policemen" of the United Nations. Many more countries joined through to the final days of the war, including colonies and former Axis nations.

After the war ended, the Allies, and the Declaration that bound them, would become the basis of the modern United Nations; one enduring legacy of the alliance is the permanent membership of the U.N. Security Council, which is made up exclusively of the principal Allied powers that won the war.