Allies of World War II in the context of "USSR"

World War II or the Second World War (1 September 1939 – 2 September 1945) was a global conflict between two coalitions: the Allies and the Axis powers. Nearly all of the world's countries participated, with many nations mobilising all resources in pursuit of total war. Tanks and aircraft played major roles, enabling the strategic bombing of cities and delivery of the first and only nuclear weapons ever used in war. World War II is the deadliest conflict in history, causing the death of 70 to 85 million people, more than half of whom were civilians. Millions died in genocides, including the Holocaust, and by massacres, starvation, and disease. After the Allied victory, Germany, Austria, Japan, and Korea were occupied, and German and Japanese leaders were put on trial for war crimes.

The causes of World War II included unresolved tensions in the aftermath of World War I, the rise of fascism in Europe and militarism in Japan. Key events preceding the war included Japan's invasion of Manchuria in 1931, the Spanish Civil War, the outbreak of the Second Sino-Japanese War in 1937, and Germany's annexations of Austria and the Sudetenland. World War II is generally considered to have begun on 1 September 1939, when Nazi Germany, under Adolf Hitler, invaded Poland, after which the United Kingdom and France declared war on Germany. Poland was divided between Germany and the Soviet Union under the Molotov–Ribbentrop Pact. In 1940, the Soviet Union annexed the Baltic states and parts of Finland and Romania. After the fall of France in June 1940, the war continued mainly between Germany, now assisted by Fascist Italy, and the British Empire, with fighting in the Balkans, Mediterranean, and Middle East, the aerial Battle of Britain and the Blitz, and the naval Battle of the Atlantic. Through campaigns and treaties, Germany gained control of much of continental Europe and formed the Axis alliance with Italy, Japan, and other countries. In June 1941, Germany invaded the Soviet Union, opening the Eastern Front and initially making large territorial gains.

Romania is a country located at the crossroads of Central, Eastern and Southeast Europe. It borders Ukraine to the north and east, Hungary to the west, Serbia to the southwest, Bulgaria to the south, Moldova to the east, and the Black Sea to the southeast. It has a mainly continental climate, and an area of 238,397 km (92,046 sq mi) with a population of 19 million people. Romania is the twelfth-largest country in Europe and the sixth-most populous member state of the European Union. Europe's second-longest river, the Danube, empties into the Danube Delta in the southeast of the country. The Carpathian Mountains cross Romania from the north to the southwest and include Moldoveanu Peak, at an altitude of 2,544 m (8,346 ft). Bucharest is the country's capital, largest urban area, and financial centre. Other major urban areas include Cluj-Napoca, Timișoara, Iași, Constanța and Brașov.

Settlement in the territory of modern Romania began in the Lower Paleolithic, later becoming the Dacian Kingdom before Roman conquest and Romanisation. The modern Romanian state was formed in 1859 with the unification of Moldavia and Wallachia under Alexandru Ioan Cuza, becoming the Kingdom of Romania in 1881 under Carol I of Romania. Romania gained independence from the Ottoman Empire in 1877, formalised by the Treaty of Berlin. After World War I, Transylvania, Banat, Bukovina, and Bessarabia joined the Old Kingdom, forming Greater Romania, which reached its largest territorial extent. In 1940, under Axis pressure, Romania lost territories to Hungary, Bulgaria, and the Soviet Union. Following the 1944 Romanian coup d'état, Romania switched sides to join the Allies. After World War II, it regained Northern Transylvania through the Paris Peace Treaties. Under Soviet occupation, King Michael I was forced to abdicate, and Romania became a socialist republic and Warsaw Pact member. After the uniquely violent Romanian revolution in December 1989, Romania began a transition to liberal democracy and a market economy.

Nazi Germany, officially the German Reich and later the Greater German Reich, was the German state between 1933 and 1945, when Adolf Hitler and the Nazi Party controlled the country, transforming it into a totalitarian dictatorship. The Third Reich, meaning "Third Realm" or "Third Empire", referred to the Nazi claim that Nazi Germany was the successor to the earlier Holy Roman Empire (800–1806) and German Empire (1871–1918). The Third Reich, which the Nazis referred to as the Thousand-Year Reich, ended in May 1945, after 12 years, when the Allies defeated Germany and entered the capital, Berlin, ending World War II in Europe.

After Hitler was appointed Chancellor of Germany in 1933, the Nazi Party began to eliminate political opposition and consolidate power. A 1934 German referendum confirmed Hitler as sole Führer (leader). Power was centralised in Hitler's person, and his word became the highest law. The government was not a co-ordinated, cooperating body, but rather a collection of factions struggling to amass power. To address the Great Depression, the Nazis used heavy military spending, extensive public works projects, including the Autobahnen (motorways) and a massive secret rearmament program, forming the Wehrmacht (armed forces), all financed by deficit spending. The return to economic stability and end of mass unemployment boosted the regime's popularity. Hitler made increasingly aggressive territorial demands, seizing Austria in the Anschluss of 1938, and the Sudetenland region of Czechoslovakia. Germany signed a non-aggression pact with the Soviet Union and invaded Poland in 1939, launching World War II in Europe. In alliance with Fascist Italy and other Axis powers, Germany conquered most of Europe by 1940 and threatened Britain.

The Axis powers, originally called the Rome–Berlin Axis and also Rome–Berlin–Tokyo Axis, was the military coalition which initiated World War II and fought against the Allies. Its principal members were Nazi Germany, the Kingdom of Italy and the Empire of Japan. The Axis were united in their far-right positions and general opposition to the Allies, but otherwise lacked comparable coordination and ideological cohesion.

The Axis grew out of successive diplomatic efforts by Germany, Italy, and Japan to secure their own specific expansionist interests in the mid-1930s. The first step was the protocol signed by Germany and Italy in October 1936, after which Italian leader Benito Mussolini declared that all other European countries would thereafter rotate on the Rome–Berlin axis, thus creating the term "Axis". The following November saw the ratification of the Anti-Comintern Pact, an anti-communist treaty between Germany and Japan; Italy joined the Pact in 1937, followed by Hungary and Spain in 1939. The "Rome–Berlin Axis" became a military alliance in 1939 under the so-called "Pact of Steel", with the Tripartite Pact of 1940 formally integrating the military aims of Germany, Italy, Japan, and later followed by other nations. The three pacts formed the foundation of the Axis alliance.

Almost every country in the world participated in World War II. Most were neutral at the beginning, but relatively few nations remained neutral to the end. World War II pitted two alliances against each other, the Allies and the Axis powers. It is estimated that 74 million people died, with estimates ranging from 40 million to 90 million dead (including all genocide casualties). The main Axis powers were Nazi Germany, the Empire of Japan, and the Kingdom of Italy; while the United Kingdom, the United States, the Soviet Union and China were the "Big Four" Allied powers.

The countries involved in or affected by World War II are listed alphabetically, with a description of their role in the conflict.

Air warfare was a major component in all theaters of World War II and, together with anti-aircraft warfare, consumed a large fraction of the industrial output of the major powers. Germany and Japan depended on air forces that were closely integrated with land and naval forces; the Axis powers downplayed the advantage of fleets of strategic bombers and were late in appreciating the need to defend against Allied strategic bombing. By contrast, Britain and the United States took an approach that greatly emphasized strategic bombing and (to a lesser degree) tactical control of the battlefield by air as well as adequate air defenses. Both Britain and the U.S. built substantially larger strategic forces of large, long-range bombers. Simultaneously, they built tactical air forces that could win air superiority over the battlefields, thereby giving vital assistance to ground troops. The U.S. Navy and Royal Navy also built a powerful naval-air component based on aircraft carriers, as did the Imperial Japanese Navy; these played the central role in the war at sea.

Strategic bombing is a systematically organized and executed military attack from the air which can utilize strategic bombers, long- or medium-range missiles, or nuclear-armed fighter-bomber aircraft to attack targets deemed vital to the enemy's war-making capability. It is a military strategy used in total war with the goal of defeating the enemy by destroying its morale, its economic ability to produce and transport materiel to the theatres of military operations, or both. The term terror bombing is used to describe the strategic bombing of civilian targets without military value, in the hope of damaging an enemy's morale.

One of the strategies of war is to demoralize the enemy so that peace or surrender becomes preferable to continuing the conflict. Strategic bombing has been used to this end. The phrase "terror bombing" entered the English lexicon towards the end of World War II and many strategic bombing campaigns and individual raids have been described as terror bombing by commentators and historians. Because the term has pejorative connotations, some, including the Allies of World War II, have preferred to use euphemisms such as "morale bombings".

The entirety of Germany was occupied and administered by the Allies of World War II, from the Berlin Declaration on 5 June 1945 to the establishment of West Germany on 23 May 1949. Unlike occupied Japan, Nazi Germany was stripped of its sovereignty and its government was entirely dissolved. After Germany formally surrendered on Tuesday, 8 May 1945, the four countries representing the Allies (the United States, United Kingdom, Soviet Union, and France) asserted joint authority and sovereignty through the Allied Control Council (ACC).

Germany after the war was a devastated country – roughly 80 percent of its infrastructure was in need of repair or reconstruction – which helped the idea that Germany was entering a new phase of history ("zero hour"). At first, Allied-occupied Germany was defined as all territories of Germany before the 1938 Nazi annexation of Austria. The Potsdam Agreement on 2 August 1945 defined the new eastern German border by giving Poland and the Soviet Union all regions of Germany east of the Oder–Neisse line (eastern parts of Pomerania, Neumark, Posen-West Prussia, East-Prussia and most of Silesia) and divided the remaining "Germany as a whole" into four occupation zones, each administered by one of the Allies.

At the end of World War II in Europe, Austria was occupied by the Allies and declared independence from Nazi Germany on 27 April 1945 (confirmed by the Berlin Declaration for Germany on 5 June 1945), as a result of the Vienna offensive. The occupation ended when the Austrian State Treaty came into force on 27 July 1955.

After the Anschluss in 1938, Austria had generally been recognized as part of Nazi Germany. In November 1943, however, the Allies agreed in the Declaration of Moscow that Austria would instead be regarded as the first victim of Nazi aggression—without denying Austria's role in Nazi crimes—and treated as a liberated and independent country after the war.