I need some facts about WW2

That's a big, broad question! Let me answer by listing a few themes and key events in connection with those themes. I'll call this outline, "Lessons of history from World War II."

Economies & governments in chaos allow extremism and strongmen to flourish.

Prior to World War II, problems in several European countries brought dictatorial leaders to power. Mussolini had come to power in Italy (1922-1929). Hitler seized power in Germany (1933/34). The Spanish Civil War (1936-1939) brought Generalissimo Franciso Franco to power in Spain, as another example of an extreme right-wing regime taking power.

Appeasement of aggressive regimes does not always produce peace.

Germany under Hitler began taking over neighboring territories. At first other international powers were not ready to do anything to stop German expansion. After the German occupation of the Rhineland (1936), incorporation of Austria (1938) and occupation of Sudetenland, the British and French prime ministers signed a pact with Hitler at Munich (September, 1938), which essentially gave him control over Czechoslovakia. They thought Hitler would stop there, but he didn't. A year later the Germans invaded Poland, which marked the beginning of World War II in Europe.

History's worst atrocities stem from looking at some other group of humans as subhuman.

The Nazis under Hitler perpetrated the Holocaust against people they viewed as lesser beings. 2 out of 3 Jews living in Europe were killed, an estimated 6 million deaths. Additional victims of the Holocaust included 2 million non-Jewish Poles, tens of thousands of Roma (gypsies), homosexuals, etc. Japan's aggression in China showed a similar pattern, in which they considered the Chinese a lesser breed of people. In late 1937 to early 1938, the Japanese army perpetrated the Nanking Massacre against Chinese victims. In a short span of time, they killed 200,000 Chinese and committed about 20,000 rapes, according to International Military Tribunal for the Far East. (Those are conservative numbers - actual totals may have been higher.

War cannot be won entirely from the air.

Germany tried to subdue Britain by air raid attacks. The Battle of Britain (July-September, 1940) was brutal, but the British people held strong under the leadership of Winston Churchill.

Invading Russia is never a good idea.

In June 1941, Operation Barbarossa began - - the German invasion of the USSR. Hitler had previously made a non-aggression pact with Stalin (the Soviet leader), but he broke it and went on the attack. The ware in the Soviet Union had millions of casualties, and Hitler's armies could not ultimately win there.

Wars of conquest eventually exhaust the conquerors.

Japan continued its aggression in the Pacific with its December 7, 1941 attack on Pearl Harbor, a US naval base. Japan had success against the US and the Allies in the Pacific until the Battle of Midway (June 1942). The tide also was turning against Germany in North Africa and in Russia. The Germans' aggression ultimately wore them out as well.

Conventional weapons can be as horrific as nuclear war.

We tend to remember most how nuclear weapons brought World War II to a very violent end. But there was much horrific violence prior to that with conventional weapons too. The Battle of Stalingrad (between Germany and the USSR) left 800,000 dead, wounded, missing, or captured on the Germany side, and over 1 million dead, wounded, missing or captured on the Soviet military side. (There were also an additional 40,000 civilian deaths. In subduing Germany, the Allies used enormous bombing raids on Germany. One example: British and American planes fire-bombed the city of Hamburg and essentially destroyed the whole city, leaving 42,600 civilians dead and 37,000 wounded. essentially destroying the entire city.

World War II in Europe ended on May 8, 1945 - "Victory in Europe (VE) Day "

World War II in the Pacific ended on September 2, 1945 - "Victory over Japan (VJ) Day" (marking Japan's formal surrender).