The Battle of Stalingrad (23 August 1942 2 February 1943) was a major battle on the Eastern Front of World War II where Nazi Germany and its allies unsuccessfully fought the Soviet Union for control of the city of Stalingrad (later renamed to Volgograd) in Southern Russia. The battle was marked by fierce close-quarters combat and direct assaults on civilians in air raids, with the battle being the epitome of urban warfare. The Battle of Stalingrad was the deadliest battle to take place during the Second World War and is one of the bloodiest battles in the history of warfare, with an estimated 2 million total casualties. Today, the Battle of Stalingrad is universally regarded as the turning point in the European Theatre of war, as it forced the Oberkommando der Wehrmacht (German High Command) to withdraw considerable military forces from other areas in occupied Europe to replace German losses on the Eastern Front. The victory at Stalingrad energized the Red Army and shifted the balance of power in the favour of the Soviets.

Stalingrad was strategically important to both sides as a major industrial and transport hub on the Volga River. Whoever controlled Stalingrad would have access to the oil fields of the Caucasus; and control of the Volga. Germany, already operating on dwindling fuel supplies focused its efforts on moving deeper into Soviet territory and taking the oil fields at any cost. On 4 August, the Germans launched an offensive by using the 6th Army and elements of the 4th Panzer Army. The attack was supported by intense Luftwaffe bombing that reduced much of the city to rubble. The battle degenerated into house-to-house fighting as both sides poured reinforcements into the city. By mid-November, the Germans, at great cost, had pushed the Soviet defenders back into narrow zones along the west bank of the river.

On 19 November, the Red Army launched Operation Uranus, a two-pronged attack targeting the weaker Romanian armies protecting the 6th Army's flanks. The Axis flanks were overrun and the 6th Army was cut off and surrounded in the Stalingrad area. Adolf Hitler was determined to hold the city at all costs and forbade the 6th Army from attempting a breakout; instead, attempts were made to supply it by air and to break the encirclement from the outside. The Soviets were successful in denying the Germans the ability to resupply through the air which strained the German forces to their breaking point. Nevertheless the German forces were determined to continue their advance and heavy fighting continued for another two months. On 2 February 1943, the German 6th army, having exhausted their ammunition and food, finally capitulated, making it the first of Hitler's field armies to surrender during World War II, after five months, one week, and three days of fighting.

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.