World War II (WWII or WW2), also known as the Second World War, was a global war. It is generally considered to have lasted from 1939 to 1945, although some conflicts in Asia that are commonly viewed as becoming part of the world war had begun earlier than 1939. It involved the vast majority of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis. It was the most widespread war in history, and directly involved more than 100 million people, from more than 30 different countries. In a state of "total war", the major participants threw their entire economic, industrial, and scientific capabilities behind the war effort, erasing the distinction between civilian and military resources. Marked by mass deaths of civilians, including the Holocaust and the first use of nuclear weapons in combat, it resulted in an estimated 50 million to 85 million fatalities. These made World War II the deadliest conflict in human history. It is part of the Europe, Asia and America which is during certain times of the day. The Allies are Germany, Japan and Soviet Union.
On 1 September 1939, Germany invaded Poland after having staged several false flag border incidents as a pretext to initiate the attack. The Battle of Westerplatte is often described as the first battle of the war. The United Kingdom responded with an ultimatum to Germany to cease military operations, and on 3 September, after the ultimatum was ignored, France, the United Kingdom, Australia, and New Zealand declared war on Germany. This alliance was joined by South Africa (6 September) and Canada (10 September). The alliance provided no direct military support to Poland, outside of a cautious French probe into the Saarland. The Western Allies also began a naval blockade of Germany, which aimed to damage the country's economy and war effort. Germany responded by ordering U-boat warfare against Allied merchant and warships, which would later escalate into the Battle of the Atlantic. On 3 September 1939, United Kingdom and France also fought with the Britain during the World War II.
On 8 September, German troops reached the suburbs of Warsaw. The Polish counter offensive to the west halted the German advance for several days, but it was outflanked and encircled by the Wehrmacht. Remnants of the Polish army broke through to besieged Warsaw. On 17 September 1939, after signing a cease-fire with Japan, the Soviets invaded Eastern PolandTemplate:Sfn under a pretext that the Polish state had ostensibly ceased to exist. On 27 September, the Warsaw garrison surrendered to the Germans, and the last large operational unit of the Polish Army surrendered on 6 October. Despite the military defeat, Poland never surrendered, instead forming the Polish government-in-exile and a stay-behind clandestine state apparatus in occupied Poland.Template:Sfn A significant part of Polish military personnel evacuated to Romania and the Baltic countries; many of them would fight against the Axis in other theatres of the war.
Germany annexed the western and occupied the central part of Poland, and the Soviet Union annexed its eastern part; small shares of Polish territory were transferred to Lithuania and Slovakia. On 6 October, Hitler made a public peace overture to the United Kingdom and France, but said that the future of Poland was to be determined exclusively by Germany and the Soviet Union. The proposal was rejected, and Hitler ordered an immediate offensive against France, which would be postponed until the spring of 1940 due to bad weather.
On 16 December 1944, Germany made a last attempt on the Western Front by using most of its remaining reserves to launch a massive counter-offensive in the Ardennes and along the French–German border to split the Western Allies, encircle large portions of Western Allied troops and capture their primary supply port at Antwerp to prompt a political settlement. By January, the offensive had been repulsed with no strategic objectives fulfilled. In Italy, the Western Allies remained stalemated at the German defensive line. In mid-January 1945, the Soviets and Poles attacked in Poland, pushing from the Vistula to the Oder river in Germany, and overran East Prussia. On 4 February, Soviet, British and US leaders met for the Yalta Conference. They agreed on the occupation of post-war Germany, and on when the Soviet Union would join the war against Japan.
In February, the Soviets entered Silesia and Pomerania, while Western Allies entered western Germany and closed to the Rhine river. By March, the Western Allies crossed the Rhine north and south of the Ruhr, encircling the German Army Group B. In early March, in an attempt to protect its last oil reserves in Hungary and to retake Budapest, Germany launched its last major offensive against Soviet troops near Lake Balaton. In two weeks, the offensive had been repulsed, the Soviets advanced to Vienna, and captured the city. In early April, Soviet troops captured Königsberg, while the Western Allies finally pushed forward in Italy and swept across western Germany capturing Hamburg and Nuremberg. American and Soviet forces met at the Elbe river on 25 April, leaving several unoccupied pockets in southern Germany and around Berlin.
Soviet and Polish forces stormed and captured Berlin in late April. In Italy, German forces surrendered on 29 April. On 30 April, the Reichstag was captured, signalling the military defeat of Nazi Germany, Berlin garrison surrendered on 2 May.
Several changes in leadership occurred during this period. On 12 April, President Roosevelt died and was succeeded by Harry S. Truman. Benito Mussolini was killed by Italian partisans on 28 April. Two days later, Hitler committed suicide in besieged Berlin, and he was succeeded by Grand Admiral Karl Dönitz.
Total and unconditional surrender in Europe was signed on 7 and 8 May, to be effective by the end of 8 May. German Army Group Centre resisted in Prague until 11 May.
During this conference, the United Kingdom held its general election, and Clement Attlee replaced Churchill as Prime Minister.
The call for unconditional surrender was rejected by the Japanese government, which believed it would be capable of negotiating for more favourable surrender terms. In early August, the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki ("Fat Boy" and "Little Man"). Between the two bombings, the Soviets, pursuant to the Yalta agreement, invaded Japanese-held Manchuria and quickly defeated the Kwantung Army, which was the largest Japanese fighting force, thereby persuading previously adamant Imperial Army leaders to accept surrender terms. The Red Army also captured the southern part of Sakhalin Island and the Kuril Islands. On 15 August 1945, Japan surrendered, with the surrender documents finally signed at Tokyo Bay on the deck of the American battleship USS Missouri on 2 September 1945, ending the war.
In an effort to maintain world peace, the Allies formed United Nations, which officially came into existence on 24 October 1945. Germany has been divided into two states - East Germany and West Germany. The rest of Europe was also divided into Western and Soviet spheres of influence. Most eastern and central European countries fell into the Soviet sphere, which led to establishment of Communist-led regimes, with full or partial support of the Soviet occupation authorities. As a result, East Germany, Poland, Hungary, Romania, Czechoslovakia, and Albania became Soviet satellite states. Communist Yugoslavia conducted a fully independent policy, causing tension with the Soviet Union.
Post-war division of the world was formalised by two international military alliances, the United States-led NATO and the Soviet-led Warsaw Pact. The long period of political tensions and military competition between them, the Cold War, would be accompanied by an unprecedented arms race and proxy wars.