World War II: The German Luftwaffe begins the Blitz, bombing London and other British cities for over 50 consecutive nights.

The Luftwaffe (German pronunciation: [lftvaf] (listen)) was the aerial-warfare branch of the German Wehrmacht before and during World War II. Germany's military air arms during World War I, the Luftstreitkrfte of the Imperial Army and the Marine-Fliegerabteilung of the Imperial Navy, had been disbanded in May 1920 in accordance with the terms of the 1919 Treaty of Versailles which banned Germany from having any air force.

During the interwar period, German pilots were trained secretly in violation of the treaty at Lipetsk Air Base in the Soviet Union. With the rise of the Nazi Party and the repudiation of the Versailles Treaty, the Luftwaffe's existence was publicly acknowledged on 26 February 1935, just over two weeks before open defiance of the Versailles Treaty through German re-armament and conscription would be announced on 16 March. The Condor Legion, a Luftwaffe detachment sent to aid Nationalist forces in the Spanish Civil War, provided the force with a valuable testing ground for new tactics and aircraft. Partially as a result of this combat experience, the Luftwaffe had become one of the most sophisticated, technologically advanced, and battle-experienced air forces in the world when World War II broke out in 1939. By the summer of 1939, the Luftwaffe had twenty-eight Geschwader (wings). The Luftwaffe also operated Fallschirmjger paratrooper units.

The Luftwaffe proved instrumental in the German victories across Poland and Western Europe in 1939 and 1940. During the Battle of Britain, however, despite inflicting severe damage to the RAF's infrastructure and, during the subsequent Blitz, devastating many British cities, the German air force failed to batter the beleaguered British into submission. From 1942, Allied bombing campaigns gradually destroyed the Luftwaffe's fighter arm. From late 1942, the Luftwaffe used its surplus ground support and other personnel to raise Luftwaffe Field Divisions. In addition to its service in the West, the Luftwaffe operated over the Soviet Union, North Africa and Southern Europe. Despite its belated use of advanced turbojet and rocket-propelled aircraft for the destruction of Allied bombers, the Luftwaffe was overwhelmed by the Allies' superior numbers and improved tactics, and a lack of trained pilots and aviation fuel. In January 1945, during the closing stages of the Battle of the Bulge, the Luftwaffe made a last-ditch effort to win air superiority, and met with failure. With rapidly dwindling supplies of petroleum, oil, and lubricants after this campaign, and as part of the entire combined Wehrmacht military forces as a whole, the Luftwaffe ceased to be an effective fighting force.

After the defeat of Germany, the Luftwaffe was disbanded in 1946. During World War II, German pilots claimed roughly 70,000 aerial victories, while over 75,000 Luftwaffe aircraft were destroyed or significantly damaged. Of these, nearly 40,000 were lost entirely. The Luftwaffe had only two commanders-in-chief throughout its history: Hermann Gring and later Generalfeldmarschall Robert Ritter von Greim for the last two weeks of the war.

The Luftwaffe was deeply involved in Nazi war crimes. By the end of the war, a significant percentage of aircraft production originated in concentration camps, an industry employing tens of thousands of prisoners. The Luftwaffe's demand for labor was one of the factors that led to the deportation and murder of hundreds of thousands of Hungarian Jews in 1944. The Oberkommando der Luftwaffe organized Nazi human experimentation, and Luftwaffe ground troops committed massacres in Italy, Greece, and Poland.

World War II or the Second World War, often abbreviated as WWII or WW2, was a global war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing military alliances: the Allies and the Axis powers. In a total war directly involving more than 100 million personnel from more than 30 countries, the major participants threw their entire economic, industrial, and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. Aircraft played a major role in the conflict, enabling the strategic bombing of population centres and the only two uses of nuclear weapons in war. World War II was by far the deadliest conflict in human history; it resulted in 70 to 85 million fatalities, a majority being civilians. Tens of millions of people died due to genocides (including the Holocaust), starvation, massacres, and disease. In the wake of the Axis defeat, Germany and Japan were occupied, and war crimes tribunals were conducted against German and Japanese leaders.

The exact causes of World War II are debated, but contributing factors included the Second Italo-Ethiopian War, the Spanish Civil War, the Second Sino-Japanese War, the Soviet–Japanese border conflicts and rising European tensions since World War I. World War II is generally considered to have begun on 1 September 1939, when Nazi Germany, under Adolf Hitler, invaded Poland. The United Kingdom and France subsequently declared war on Germany on 3 September. Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union had partitioned Poland and marked out their "spheres of influence" across Finland, Estonia, Latvia, Lithuania and Romania. From late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or controlled much of continental Europe, and formed the Axis alliance with Italy and Japan (along with other countries later on). Following the onset of campaigns in North Africa and East Africa, and the fall of France in mid-1940, the war continued primarily between the European Axis powers and the British Empire, with war in the Balkans, the aerial Battle of Britain, the Blitz of the UK, and the Battle of the Atlantic. On 22 June 1941, Germany led the European Axis powers in an invasion of the Soviet Union, opening the Eastern Front, the largest land theatre of war in history.

Japan, which aimed to dominate Asia and the Pacific, was at war with the Republic of China by 1937. In December 1941, Japan attacked American and British territories with near-simultaneous offensives against Southeast Asia and the Central Pacific, including an attack on the US fleet at Pearl Harbor which resulted in the United States declaring war against Japan. Therefore the European Axis powers declared war on the United States in solidarity. Japan soon captured much of the western Pacific, but its advances were halted in 1942 after losing the critical Battle of Midway; later, Germany and Italy were defeated in North Africa and at Stalingrad in the Soviet Union. Key setbacks in 1943—including a series of German defeats on the Eastern Front, the Allied invasions of Sicily and the Italian mainland, and Allied offensives in the Pacific—cost the Axis powers their initiative and forced it into strategic retreat on all fronts. In 1944, the Western Allies invaded German-occupied France, while the Soviet Union regained its territorial losses and turned towards Germany and its allies. During 1944 and 1945, Japan suffered reversals in mainland Asia, while the Allies crippled the Japanese Navy and captured key western Pacific islands.

The war in Europe concluded with the liberation of German-occupied territories, and the invasion of Germany by the Western Allies and the Soviet Union, culminating in the fall of Berlin to Soviet troops, Hitler's suicide and the German unconditional surrender on 8 May 1945. Following the Potsdam Declaration by the Allies on 26 July 1945 and the refusal of Japan to surrender on its terms, the United States dropped the first atomic bombs on the Japanese cities of Hiroshima, on 6 August, and Nagasaki, on 9 August. Faced with an imminent invasion of the Japanese archipelago, the possibility of additional atomic bombings, and the Soviet’s declared entry into the war against Japan on the eve of invading Manchuria, Japan announced on 15 August its intention to surrender, then signed the surrender document on 2 September 1945, cementing total victory in Asia for the Allies.

World War II changed the political alignment and social structure of the globe. The United Nations (UN) was established to foster international co-operation and prevent future conflicts, with the victorious great powers—China, France, the Soviet Union, the United Kingdom, and the United States—becoming the permanent members of its Security Council. The Soviet Union and the United States emerged as rival superpowers, setting the stage for the nearly half-century-long Cold War. In the wake of European devastation, the influence of its great powers waned, triggering the decolonisation of Africa and Asia. Most countries whose industries had been damaged moved towards economic recovery and expansion. Political and economic integration, especially in Europe, began as an effort to forestall future hostilities, end pre-war enmities and forge a sense of common identity.