Humanity's best and worst were displayed for all the world to see.note Clockwise from top: Allied troops land in France during Operation Overlord; Arbeit macht frei ("Work will free you") over the entrance to Auschwitz Death-Camp; the Soviet flag is raised over the Reichstag; the atomic bomb attack on Hiroshima; a Nazi party parade.
— Joseph Goebbels, Sportpalast speech, 18 February 1943
World War II, or the Second World War (often abbreviated as WWII or WW2), was a global war fought from 1939 to 1945. It involved the vast majority of the world's nations and nation-states — including all the great powers — which eventually formed two loose, opposing military alliances: the Allies or Allied powers (China, France, the UK, the USA, the USSR among others) against the Axis powers (chiefly Nazi Germany, Fascist Italy and Imperial Japan).
World War II is most commonly described as having been fought in two main theaters of war. The European Theater was the conflict between the Allied Powers against Germany, Italy and their European allies. This conflict was fought not only in Europe, but in the Atlantic Ocean and North Africa. This conflict began with the invasion of Poland in September of 1939 and ended in May 1945 with the fall of Berlin and Prague. The Pacific Theater was the conflict fought between the Allies and Imperial Japan in the Pacific Ocean and Asia, which also included some action in the Indian Ocean. This conflict was born out of the Second Sino-Japanese War which started when the Japanese Empire invaded China in July 1937. This war became part of the 'world war' proper when Japan attacked American and British territories in December 1941.
It was the most intensive and extensive war in history, with more than 100 million people serving in military units. In a state of "total war", the major participants eventually placed their entire financial, industrial, and scientific capabilities at the service of the war effort, thereby erasing the distinction between civilian and military resources. Marked by significant events involving (organized) massacres and genocides, including the Holocaust, large-scale aerial bombardment of civilian populations and the only use of nuclear weapons in warfare, it resulted in some 50 to 70 million dead (some higher estimates go to a nice round 100 million by counting the unborn... or just by simple, and usually not deliberate, miscountingnote One infamous error made by someone compiling figures for military dead, missing, and wounded in the Soviet-German War/Ostfront was made by someone missing a zero, thereby claiming that a Soviet force lost more troops in a single operation/campaign than there were in the entire Red Army. Someone else also arrived at an infamous estimate of 40+ million Soviet dead (versus a usual estimate of no more than 28 million) during the war by effectively mis-counting 'wounded' soldiers as 'dead' soldiers (no more than 20-30% of 'wounded' soldiers died at any point; this guy assumed that it was considerably more than that) and failing to account for the Poles ethnically cleansed (forcibly evicted) from the western USSR in the immediate post-war period. Although the USSR was supposedly his specialty, he also put Chinese dead at 30-40 million (versus a usual estimate of no more than c.10-20 million) by choosing the highest possible estimate of war-dead and attributing the c.10 million dead of the later Chinese Civil War and post-war CCP purges (1946-50) to the Sino-Japanese War (1937-45). This is how he managed to arrive at a figure of 100 million dead, even though there's really no way it could've been more than 70. ) - making this war the deadliest and costliest conflict in human history.
America Wins the War: The US's media depictions of the war are often accused of ignoring the contributions of other states, nations, and nation-states to (winning) the war - with the USSR's pivotal role in particular being almost completely ignored due to (lingering) Cold-Waranti-Communist sentiment. Post-Soviet Russian media might now quite justly be accused of Russia Wins The War due to it ignoring both the contributions of the other republics that made up the USSR (Ukraine, Estonia, etc.. etc.) as well as all the other countries and peoples who fought The Axis.
A somewhat related phenomenon is that the only Axis troops ever seen in most media are the Germans - the Italians very rarely make an appearance, and the Hungarians, Slovaks, Romanians, Bulgarians, and Finns are almost entirely absent.
Cheese-Eating Surrender Monkeys: The Trope Maker in the world's consciousness. The truth is a lot more complex. While few people (like General de Gaulle) saw the point in fighting on once France had 'already lost' The Battle Of France - Marshall Pétain's coup had a lot of popular support - and they saw no hope of Germany ever being defeated. But once they became certain that Germany would lose the war (Stalingrad, North Africa, Kursk) resistance groups were founded and were ready to welcome The Allies' return with some of the best espionage work the world has ever seen. General de Gaulle's Free French Forces also contributed several thousand combat troops to battles such as Bir Hakeim, Monte Cassino and Ouistreham (on Operation Overlord's D-Day), and once France was liberated they formed an army several hundred thousand strong to take over support roles and free up Anglo-American troops for the front lines.
It should be noted the image most people gained from the popular media (crematoria, burning pits, gas chambers, fierce guards with dogs, experiments on people and so on) comes from the final phase of the Holocaust, the extermination of Hungarian and Transylvanian Jews, when the death industry finally broke down overloaded with dead bodies. This is the plain reason for which we have survivors to tell the tales, because at that moment there were people to escape or survive. Previous campaigns of mass murder (euthanasia of the mentally disabled, extermination of the Soviet prisoners, extermination of Jews in Operation Reinhard camps in Poland) were so efficient they barely left any survivors.
"Auschwitz was a walk in the park compared to Treblinka" - Hershl Sperling, Holocaust survivor
La Résistance: The Trope Namer was active during this war in France, but every occupied country had a resistance movement to one degree or another. Some countries actually had more than one movement - e.g. a communist one plus a monarchist one (it wasn't unusual for them to end up fighting each other as well). China had so many turncoats-turned-resistance fighters-turned-bandits that the historical community generally wrings its hands and splits it up into local and regional warlords, nationalist guerrillas, communist guerrillas and Chinese Communist Party guerrillas, with some room for overlap.
No Swastikas: The entire rationale behind the taboos on the swastika and the Rising Sun, in fact.
The Quisling: Trope NamerVidkun Quisling, who betrayed his country to the Nazis and got stood up in front of a firing squad after the war. Other Quislings of World War II include President Wang Jingwei, Marshal Philippe Pétain and Prime Minister Pierre Laval of France and General Andrei Vlasov of The Soviet Union. Quisling, Laval and Vlasov were (tortured and) executed, Pétain's death sentence was commuted to life imprisonment due to his advanced age and (by that time) severe dementia, and Jingwei died of natural causes before the war was over.
The Jericho Trumpet was removed from later models of the Stuka, as the Germans quickly came to the conclusion that equipping a bomber with its own air raid siren to warn the enemy was counter-productive.
Stupid Jetpack Hitler: Nazi Germany developed some advanced technologies that were ahead of their time, such as the first operational jet airplanes, ballistic missiles and cruise missiles. German scientists also played a key role in the development of the US and Soviet ballistic missile and space programs after the war. But no jetpacks.
Those Wacky Nazis: The trope became popular because of the German occupation of Europe, the Nazis' war crimes and the Holocaust.