series of coordinated suicide attacks by al-Qaeda upon the United States on September 11, 2001. On that morning, 19 al-Qaeda terrorists hijacked four commercial passenger jet airliners. The hijackers intentionally crashed two of the airliners into the Twin Towers of the World Trade Center in New York City, killing everyone on board and many others working in the buildings. he hijackers crashed a third airliner into the Pentagon in Arlington, Virginia, just outside Washington, D.C. The fourth plane crashed into a field near Shanksville in rural Pennsylvania. http://en.wikipedia.org/wiki/September_11_attacks
In September 1962, after some unsuccessful operations by the U.S. to overthrow the Cuban regime the Cuban and Soviet governments began to surreptitiously build bases in Cuba for a number of medium-range and intermediate-range ballistic nuclear missiles with the ability to strike most of the continental United States. http://en.wikipedia.org/wiki/Cuban_Missile_Crisis
military conflict between the Republic of Korea, supported by the United Nations, and the Democratic People's Republic of Korea, supported by the People's Republic of China, with military material aid from the Soviet Union.
The war was a result of the physical division of Korea by an agreement of the victorious Allies at the conclusion of the Pacific War at the end of World War II. http://en.wikipedia.org/wiki/Korean_War
Global military conflict lasting from 1939 to 1945, which involved most of the world's nations, including all of the great powers: eventually forming two opposing military alliances, the Allies and the Axis. http://en.wikipedia.org/wiki/World_War_II
This conflict involved all of the world's great powers, assembled in two opposing alliances: the Allies (centered around the Triple Entente) and the Central Powers. http://en.wikipedia.org/wiki/World_War_I