Led by Adolf Hitler, Emperor Hirohito, and Benito Mussolini (Axis).
The Axis Power's primary members was Nazi Germany (Adolf Hitler), Imperial Japan (Emperor Hirohito), and Fascist Italy (Benito Mussolini), as well as some smaller countries, including Hungary, Romania, etc.
Invaded Normandy on D-Day (Allies).
Normandy was invaded in Operation Overlord on June 6, 1944, and comprised of 5 beaches, Utah and Omaha beach tasked under American Forces, Sword and Gold beach under British forces, and Juno under Canadian forces.
Signed the Tripartite Pact (Axis).
The Tripartite Pact was signed by Germany, Italy, Hungary, Bulgaria, Romania, etc., and later the last major power Japan. It was a military pact.
Luftwaffe conducted aerial warfare (Axis).
The Luftwaffe is the official name of the German Air Corps during World War II.
Bombed Hiroshima and Nagasaki (Allies).
The US created the Atomic bomb, in which 1 was dropped in the Nevada Test Site, and the next two in first Hiroshima, and then Nagasaki.
Conquered Poland (Axis + Ally-to-be turncoat).
The U.S.S.R was technically part of the Axis Power in the beginning of the war with the Molotov-Ribbentrop Pact between the U.S.S.R and Nazi Germany, which stated that the U.S.S.R will take over the eastern half of Poland, with Germany taking the western half.
Attack on Pearl Harbor (Axis).
Pearl Harbor was attacked December 7th, 1941 by the Japanese Imperial Naval air force, which was the reason for the US to join the War completely. It is worth noting that the Japanese missed out on the carriers as they were not in Pearl Harbor during that time (out doing exercise), and later it will prove that the aircraft carriers would play a indispensable role in the Pacific front.
Member Nations included France and England (Allies).
France was a part of the Allies until it capitulated against the Nazi blitzkrieg, in which it was split in two, with the official French government (Free French F.F.) setting up in Great Britain and de facto ruled France, while Vichy France were French allies to the Axis power.
RAF conducted aerial warfare (Allies).
The R.A.F. (or Royal Air Force), was the military air force for Great Britain, and played a well-known role in the Battle of Britain, fighting off German bombers and fighters, making Germany call off it's invasion of Great Britain.
Invaded the Soviet Union (Axis).
The Axis Powers, primarily Germany, launched Operation Barbarossa, which led to the invasion of the Soviet Union by Germany during the summer. It ended with a Soviet pyrrhic victory, as German lines were stretched, they were not adequately supplied, and they were not dressed for weather conditions.
Fought island-hopping campaign in the Pacific (Allies).
The island-hopping campaign was used primarily by the United States and Australia, and set about only taking strategic and/or large islands to build airfields on to strike out on the Japan mainland. One interesting note is that the Philippines was not actually part of the plan, but McArthur decided to liberate Philippines after promising them that he would be back.
Why do historians call the people who served in World War II "The Greatest Generation"?
Historians called the people who served in World War II The Greatest Generation, as ordinary citizens were called upon by their countries to fight for their nationalistic ideologies. It saw to people having to not only rebuild their lives following the Great Depression, but also to defend their way of life, whether danger was imminent or far away. Regardless, most people did their nationalistic duties and helped with their countries war effort one way or another.