The Allies of World War II were the countries that opposed the Axis powers during the Second World War (1939–1945). The Allies promoted the alliance as seeking to stop German, Italian and Japanese 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, Newfoundland and South Africa.)[1] After first having cooperated with Germany in partitioning Poland whilst remaining neutral in the Allied-Axis conflict, the Soviet Union joined the Allies in June-1941 after being invaded by Germany and its allies. The United States joined in December 1941 after the Japanese attack on Pearl Harbor. As of 1942, the “Big Three” leaders of Britain, the Soviet Union, and the United States controlled Allied policy; relations between Britain and the U.S. were especially close. Other key Allies included China, Canada, British Raj (India), the Netherlands, Norway 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).

Origins and creation

Main article: Causes of World War II

The origins of the Allied powers stem from the Allies of World War I and cooperation of the victorious powers at the Paris Peace Conference, 1919. Germany deeply resented being forced to sign the Treaty of Versailles. The new Weimar republic’s legitimacy became shaken. However the 1920s were peaceful.

With the Stock Market Crash of 1929 and the ensuing Great Depression, political unrest in Europe soared including the rise in support of revanchist nationalists in Germany who blamed the severity of the economic crisis on the Treaty of Versailles. By the early 1930s, the Nazi Party led by Adolf Hitler became the dominant revanchist movement in Germany and Hitler and the Nazis gained power in 1933. The Nazi regime demanded the immediate cancellation of the Treaty of Versailles, and made claims to German-populated Austria, and German-populated territories of Czechoslovakia. The likelihood of war was high, and the question was whether it could be avoided through strategies such as Appeasement.

In Asia, when Japan seized Manchuria in 1931, the League of Nations condemned it for aggression against China. Japan responded by leaving the League of Nations in March 1933. After four quiet years, the Sino-Japanese War erupted in 1937 with Japanese forces invading China. The League of Nations condemned Japan’s actions and initiated sanctions on Japan. The United States in particular was angered at Japan and sought to support China.

In March 1939, Germany invaded Czechoslovakia, violating the Munich Agreement signed six months before, and demonstrating that appeasement was a failure. Britain and France decided that Hitler had no intention to uphold diplomatic agreements and responded by preparing for war. They tried in 1939 tried to avert a German move east by promising go to war with Germany if it invaded Poland, and seeking an alliance with the USSR. Hitler ended the risk of a war with Stalin by a non-aggression pact with the USSR in August 1939. It secretly divided the independent nations of eastern Europe between the two powers and assured adequate oil supplies for the German war machine. On 1 September 1939, Germany invaded Poland; two days later Britain and France declared war on Germany. Poland fell in a matter of days. A government in exile was set up and it became one of the Allies, a model followed by other invaded countries. After a quiet winter Germany in April 1940 invaded and quickly defeated Scandinavia, Belgium, Holland and France. Britain and its Empire stood alone against Hitler and Mussolini. In June 1941, however., Germany invaded the USSR. In December Japan attacked the US and Britain. The main lines of World War II had formed.

Major affiliated state combatants

Main article: Diplomatic history of World War II

During December 1942, U.S. President Franklin D. Roosevelt devised the name “United Nations” for the Allies. He referred to the Big Three and China as a “trusteeship of the powerful”, and then later the “Four Policemen”.  The Declaration by United Nations on 1 January 1942 was the basis of the modern United Nations (UN). At the Potsdam Conference of July–August 1945, Roosevelt’s successor, Harry S. Truman, proposed that the foreign ministers of China, France, the Soviet Union, United Kingdom, and the United States “should draft the peace treaties and boundary settlements of Europe”, which led to the creation of the Council of Foreign Ministers.

Soviet Union

  • Soviet soldiers and T-34 tanks advance in skirmish near Bryansk in 1942.
  • Soviet soldiers fighting in the ruins of Stalingrad during the Battle of Stalingrad.
  • Soviet Il-2 ground attack aircraft attacking German ground forces during the Battle of Kursk.
  • Soviet Katyusha multiple rocket launchers fire in Berlin, April 1945 during the Battle of Berlin.

War justifications

General Secretary Joseph Stalin and the government of the Soviet Union justified the Soviet war effort that resulted from the German invasion of the Soviet Union with Operation Barbarossa in 1941, as a defensive war being fought by patriotic Soviet people for their survival.[6] Stalin had supported popular front movements of anti-fascists including communists and non-communists from 1935 to 1939. The popular front strategy was terminated from 1939 to 1941 when the Soviet Union cooperated with Germany in 1939 in the occupation and partitioning of Poland while the Soviet Union refused to endorse either the Allies or the Axis from 1939 to 1941, as it called the Allied-Axis conflict an “imperialist war”. After the invasion of the Soviet Union in 1941, Stalin endorsed the Western Allies as part of a renewed popular front strategy against Germany and called for the international communist movement to make a coalition with all those who opposed the Nazis.

The Soviet Union intervened against Japan and its client state in Manchuria in 1945, cooperating with the Nationalist Government of China and Nationalist Party led by Chiang Kai Shek; though also cooperating, preferring, and encouraging the Communist Party led by Mao Zedong to take effective control of Manchuria after expelling Japanese forces.


On 20 August 1939, forces of the Union of Soviet Socialist Republics under General Georgy Zhukov, together with the People’s Republic of Mongolia eliminated the threat of conflict in the east with a decisive victory over Japan at the Battle of Khalkhin Gol in eastern Mongolia.

On the same day, Soviet party leader Joseph Stalin received a telegram from German Chancellor Adolf Hitler, suggesting that German Foreign Minister Joachim von Ribbentrop fly to Moscow for diplomatic talks. (After receiving a lukewarm response throughout the spring and summer, Stalin abandoned attempts for a better diplomatic relationship with France and the United Kingdom.)

On 23 August, Ribbentrop and Soviet Foreign Minister Vyacheslav Molotov signed the non-aggression pact including secret protocols dividing Eastern Europe into defined “spheres of influence” for the two regimes, and specifically concerning the partition of the Polish state in the event of its “territorial and political rearrangement”.

On 15 September 1939, Stalin concluded a durable ceasefire with Japan, to take effect the following day (it would be upgraded to a nonaggression pact in April 1941).  The day after that, 17 September, Soviet forces invaded Poland from the east. Although some fighting continued until 5 October, the two invading armies held at least one joint military parade on 25 September, and reinforced their non-military partnership with a German–Soviet Treaty of Friendship, Cooperation and Demarcation on 28 September.

On 30 November, the Soviet Union attacked Finland, for which it was expelled from the League of Nations. In the following year of 1940, while the world’s attention was focussed upon the German invasion of France and Norway,  the USSR militarily occupied the Baltic states of Estonia, Latvia and Lithuania as well as parts of Romania.

German-Soviet treaties were brought to an end by the German surprise attack on the USSR on 22 June 1941. The Soviet Union so entered in alliance with the United Kingdom. Following the USSR, a number of other communist, pro-Soviet or Soviet-controlled forces fought against the Axis powers during the Second World War. They were as follows: the Albanian National Liberation Front, the Chinese Red Army, the Greek National Liberation Front, the Hukbalahap, the Malayan Communist Party, the People’s Republic of Mongolia, the Polish People’s Army, the Tuvan People’s Republic (annexed by Soviet Union in 1944),[15] the Viet Minh and the Yugoslav Partisans.