Alliance

An alliance is a relationship among people, groups, or states that have joined together for mutual benefit or to achieve some common purpose, whether or not explicit agreement has been worked out among them. Members of an alliance are called allies. Alliances form in many settings, including political alliances, military alliances, and business alliances. When the term is used in the context of war or armed struggle, such associations may also be called allied powers, especially when discussing World War I or World War II.

A formal military alliance is not required for being perceived as an ally—co-belligerence, fighting alongside someone, is enough. According to this usage, allies become so not when concluding an alliance treaty but when struck by war.

When spelled with a capital "A", the word "Allies" usually denotes the countries who fought together against the Central Powers in World War I (the Allies of World War I), or those who fought against the Axis Powers in World War II (the Allies of World War II). The term has also been used by the United States Army to describe the countries that gave assistance to the South Vietnam during the Vietnam War.

Allies of World War II

The Allies of World War II, called the United Nations from the 1 January 1942 declaration, were the countries that together opposed the Axis powers during the Second World War (1939–1945). The Allies promoted the alliance as seeking to stop German, Japanese and Italian aggression.

The anti-German coalition at the start of the war (1 September 1939) consisted of France, Poland and Great Britain, soon to be joined by the British Commonwealth (Canada, Australia, New Zealand and South Africa). Poland was a minor factor after its defeat in 1939; France was a minor factor after its defeat in 1940. After first having cooperated with Germany in partitioning Poland whilst remaining neutral in the Allied-Axis conflict, the Soviet Union perforce joined the Allies in June 1941 after being invaded by Germany. The United States provided war materiel and money all along, and officially joined in December 1941 after the Japanese attack on Pearl Harbor. As of 1942, the "Big Three" leaders of the United Kingdom, the Soviet Union, and the United States controlled Allied policy; relations between the United Kingdom and the United States were especially close. China had been already at war with Japan since the Marco Polo Bridge Incident of 1937 but officially joined the Allies in 1941. The Big Three and China were referred as a "trusteeship of the powerful", then were recognized as the Allied "Big Four" in Declaration by United Nations and later the "Four Policemen" of "United Nations" for the Allies. Other key Allies included British India, the Netherlands, and Yugoslavia as well as Free France; there were numerous others. Together they called themselves the "United Nations" and in 1945 created the modern UN.

Allies of World War I

The Allies of World War I, also known as the Allied Powers, were the countries that opposed the Central Powers during the First World War.

The members of the original Entente Alliance of 1907 were the French Republic, the British Empire and the Russian Empire. Italy ended its alliance with the Central Powers, arguing that Germany and Austria-Hungary started the war and that the alliance was only defensive in nature; it entered the war on the side of the Entente in 1915. Japan was another important member. Belgium, Serbia, Greece, Montenegro, and Romania were affiliated members of the Entente.

The 1920 Treaty of Sèvres defines as the Principal Allied Powers: British Empire, French Republic, Italy and Japan. The Allied Powers comprised – together with the Principal Allied Powers – Armenia, Belgium, Greece, Hejaz, Poland, Portugal, Romania, Serb-Croat-Slovene state and Czechoslovakia.

The United States declared war on Germany in April 1917 on the grounds that Germany had violated U.S. neutrality by attacking international shipping and because of the Zimmermann Telegram sent to Mexico. It declared war on Austria-Hungary in December 1917. The U.S. entered the war as an "associated power", rather than as a formal ally of France and the United Kingdom, in order to avoid "foreign entanglements". Although the Ottoman Empire and Bulgaria severed relations with the United States, neither declared war on her.