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The European theatre of World War II was one of the two main theatres of combat during World War II, lasting from September 1939 to May 1945. The Allied powers (including the United Kingdom, the United States, the Soviet Union and France) fought the Axis powers (including Nazi Germany and the Kingdom of Italy) on both the Western and Eastern fronts across the continent. There was also significant conflict in the Scandinavian, Mediterranean, and Balkan regions. The war was intense, resulting in at least 39 million deaths and bringing about a dramatic change in the balance of power on the continent.
During the 1930s, Adolf Hitler, the leader of Nazi Germany, expanded German territory by annexing Austria and the Sudetenland region of Czechoslovakia in 1938. This expansion was motivated in part by Germany's racial ideology, which held that the country needed to expand for the so-called "Aryan race" to survive. Hitler was aided by Italy, another fascist state led by Benito Mussolini. World War II began with Germany's invasion of Poland on 1 September 1939.
Poland's allies, France and the United Kingdom, declared war on Germany days after the invasion of Poland but were unwilling to engage in active combat. The Soviet Union, led by Joseph Stalin and having signed a non-aggression pact with Germany, invaded eastern Poland; the two nations then partitioned Poland between them. This situation changed after Germany invaded Norway, Denmark, France, the Netherlands, Belgium, and Luxembourg. These six countries were quickly overrun, and Germany began two successive aerial bombardments of the United Kingdom: the Battle of Britain and the Blitz. British prime minister Winston Churchill led his country's war effort. Germany also initiated the genocide of Jews, known as the Holocaust. In 1940, Italy invaded Greece, and in 1941, Germany invaded Yugoslavia and Greece. In June 1941, Germany began an invasion of the Soviet Union, and in December 1941, Germany declared war on the United States, shortly after Imperial Japan did so. The United States was led by President Franklin D. Roosevelt.
In 1942, the Soviets halted the German invasion of their country at the Battle of Stalingrad. Meanwhile, the Allies conducted a mass bombing campaign against German industrial targets. In 1943, the Allied powers began an invasion of Italy, leading to the end of Mussolini's regime, but Germans and Italians loyal to the Axis continued fighting. The Allies liberated Rome in June 1944. Also in June, the Allied powers began an invasion of German-occupied Western Europe, while the Soviets launched a massive counteroffensive in Eastern Europe. Both campaigns were successful for the Allies. The Soviet Union captured much of Central and Eastern Europe, including the German capital Berlin, while Mussolini was hanged and Hitler committed suicide. The concentration camps used in the Holocaust were liberated. In April 1945, Roosevelt died and was succeeded by Harry S. Truman. Germany unconditionally surrendered on 8 May 1945, although fighting continued in other parts of Europe until 25 May. On 5 June 1945, the Berlin Declaration, proclaiming the unconditional surrender of Germany to the four victorious powers, was signed. The Allied powers then turned their attention to finishing the Pacific War against Japan.
Once World War II ended, the Allies occupied much of the European continent, restoring some countries back to their pre-war leaders or establishing new governments, before funding their nations' economic recovery. German military leaders were put on trial at the Nuremberg trials. Western Europe became a bloc of capitalist governments, while Eastern Europe became communist, marking the beginning of the Cold War among the former Allied nations. Germany was divided into capitalist West Germany and communist East Germany.
Background
Axis powers
Germany was defeated in World War I, and the 1919 Treaty of Versailles placed punitive conditions on the country after finding Germany and the other Central Powers guilty for starting the war. These punishments included the loss of Alsace-Lorraine, the temporary loss of the Saarland, military limitations, and reparation payments to the Allied powers. The Rhineland region of Germany was also made a demilitarised zone. Germany would also join the League of Nations, an international governmental body devoted to peacekeeping. Historians are divided on whether or not the treaty was harsh or actually "very restrained" compared to other peace treaties at the time. Many Germans back then blamed their country's post-war economic collapse on the treaty's conditions and these resentments contributed to the political instability, which made it possible for Adolf Hitler and his Nazi Party to come to power. This was worsened by the worldwide Great Depression, which began in 1929.
Hitler became the chancellor and fuhrer of Germany in 1933. In February 1933, the German Reichstag building caught on fire in an arson attack, giving Hitler the opportunity to blame the fire on his political opponents, especially communists. In response, the government passed the Decree of the Reich President for the Protection of the People and State, which "abolished freedom of speech, assembly, privacy and the press; legalized phone tapping and interception of correspondence; and suspended the autonomy of federated states, like Bavaria". Communist politicians were arrested, leaving the Nazi Party free to do what they wanted. Hitler made Germany an absolute dictatorship, and he withdrew from the League of Nations.
From 1919 to 1921, Italian fascist Benito Mussolini grew a base of supporters who wanted him to deal with Italy's political and economic crises, which involved civil conflict over the growth of socialism in the country. Many of Mussolini's supporters became known as blackshirts, who would form a paramilitary that terrorised the Italian countryside in a campaign against socialism. In 1922, during a controversial general strike by a weakened trade unionist movement, Mussolini and his followers seized power in Rome and installed him as the Prime Minister of Italy to run the country alongside the pre-existing monarchy of King Victor Emmanuel III. Similar to Germany, Mussolini turned the country into a one-party fascist state which outlawed free speech, the free press, trade unions, and targeted socialists, Catholics, and liberals with a network of secret police and spies. Italy became sympathetic to Nazi Germany in the 1930s.
thumb|A celebration at the 1940 Tokyo signing of the [[Tripartite Pact|Tripartite Act defence agreement between Nazi Germany, Imperial Japan, and Fascist Italy; their flags are present|upright=1.36]]
Italy, Germany, and Imperial Japan — led by Emperor Hirohito and Prime Minister Hideki Tojo — increasingly allied with each other, and during World War II they would be known as the Axis powers. Italy and Japan needed allies, as Italy was involved in the Second Italo-Ethiopian War (the Italian invasion of the Ethiopian Empire) from 1935 to 1937, and Japan started the Second Sino-Japanese War (Japan's expanded invasion of the Republic of China) in 1937, the latter of which was subsumed by World War II and ended in 1945.
In 1936, Italy and Germany made a pact of mutual assurance, the Rome-Berlin Axis agreement. Also that year, Japan and Germany signed the Anti-Comintern Pact to counter the perceived threat of communism from the Soviet Union led by Joseph Stalin; Italy joined the pact in 1937. Italy and Germany signed the Pact of Steel in 1939, formalising the Rome-Berlin axis. Other smaller powers joined the Axis throughout World War II. The Axis' main opponents would be the Allies, a name reused from the Allies who were the main opponent of the Central Powers in World War I.
Nazi social policies
Under the Nazi Party, Germany developed a hierarchy which considered the pseudoscientific "Aryan race" — white ethnic Germans or those closest genetically to them – as the most superior race, and Jews and Slavs at or near the bottom. A major part of Nazi Germany's racial policy was the concept of lebensraum, or "living space": increasing the amount of land in Europe where members of the Aryan race could live. The United States Holocaust Memorial Museum writes:
thumb|The boundaries of the "[[Greater Germanic Reich" that the Nazi Party planned to be occupied by the "Aryan race", who were alleged to require "living space" (lebensraum) in Europe beyond Germany's borders|300x300px]]This formed a key motivation of Germany's expansion in Europe in the mid-to-late 1930s. In 1934, Germany signed a non-aggression pact with Poland, but this would not last as Poland was considered a part of the lebensraum; Nazi mythology considered eastern Europe to be lost German land. In 1933, Germany began building concentration camps to hold their political enemies and those they considered "degenerates", such as people on the lower end of their racial hierarchy, the Nazi Party's political enemies (like socialists, social democrats, and communists), Poles, Romani people, Jehovah's Witnesses, Freemasons, disabled people, and LGBTQ people. They were brought from many places across lower continental Europe to the camps using the extensive railway network which crossed the continent. In 1938, during the Kristallnacht pogroms, 30,000 Jews were sent to concentration camps.
In 1938, German chemists Otto Hahn and Fritz Strassman discovered nuclear fission, or the release of large amounts of energy when an atom's nucleus splits into smaller nuclei. German scientists of the Uranverein (uranium club) then began a project to develop the atomic bomb, a bomb using nuclear fission that could destroy entire cities. This was supposed to be secret, but scientists fleeing Nazi Germany to avoid persecution made word of the program in other Western countries. In 1939, United States President Franklin D. Roosevelt was warned of the program by one of these fleeing scientists, Albert Einstein.
German expansion and the partition of Czechoslovakia
The UK and France responded to Germany's aggressive expansion through appeasement, "maintain[ing] peace in Europe by making limited concessions to German demands", which was seen as reasonable by the British and French populaces because the Treaty of Versailles was thought of as indeed too restrictive, and they did not want to go to war with Germany.
Hitler then threatened to go to war with Czechoslovakia, and in response, on 30 September 1938, Hitler, Mussolini, UK prime minister Neville Chamberlain, and French premier Edouard Daladier signed the Munich Agreement, which gave Germany the Sudetenland, a Czech region near its border with Germany which had long been ethnically German. Chamberlain returned to England and proclaimed that the UK had achieved "Peace for our time". Later that month, part of Slovakia became the independent fascist and Catholic state of the Slovak Republic under dictator and Catholic priest Jozef Tiso. The republic was controlled by the Slovak People's Party, who made the country a client state of Germany and allowed Germany to occupy it. Hitler gave the orders to invade on 26 August, certain that the UK and the Soviet Union would not retaliate. However, on the 25th, the UK and Poland publicly signed a formal treaty of military assurance, causing Hitler to delay the war for a few days. On 31 August, he gave the order to invade the next day. In 1939, they surpassed the three current Allied powers in their individual numbers of infantry and armoured divisions (the Wehrmacht<nowiki/>'s armoured divisions are also known as panzer divisions).