1939-1945 AD
Major international conflict in Earth's 20th Century.
The nation-states involved were:
Belgium, Brazil, Australia, Canada, India, New Zealand, South Africa, United Kingdom, China, Czechoslovakia, Denmark, France, Greece, Netherlands, Norway, Poland, Philippines, United States, U.S.S.R., and Yugoslavia.
fighting against:
Bulgaria, Finland, Germany, Hungary, Italy, Japan, and Romania.
27 nations in all were officially engaged in this war which touched every inhabited continent on Earth. The war killed 37,215,153 people not counting the more than 6,000,000 innocents killed in the Nazi genocide camps.
World War II produced signifigant effects on the history of humans. The Atom Bomb was invented, harnessing the awesome power of nuclear fission. Also, the United Nations organization was founded to help prevent future conflicts by creating a forum for nations to address their grievances peacefully.
The United Nations eventually came to be the governing body of Earth and is the signatory authority which bound Earth to the charter of the United Federation of Planets.