<P> Two wars and a near - war in the 1950s became the focus for capitalist versus communist struggle . The first war was the Korean War, fought between People's Republic of China - backed North Korea and mainly United States - backed South Korea . North Korea's invasion of South Korea led to United Nations intervention . General Douglas MacArthur led troops from the United States, Canada, Australia, Great Britain, and other countries in repulsing the Northern invasion . However, the war reached a stalemate after Chinese intervention pushed U.N. forces back, and an Armistice ended hostilities, leaving the two Koreas divided and tense for the rest of the century . </P> <P> The second war, the Vietnam War, was perhaps the second most visible war of the 20th century, after World War II . After the French withdrawal from its former colony, Vietnam became partitioned into two halves, much like Korea . Fighting between North and South eventually escalated into a regional war . The United States provided aid to South Vietnam, but was not directly involved until the Gulf of Tonkin Resolution, passed in reaction to a supposed North Vietnamese attack upon American destroyers, brought the U.S. into the war as a belligerent . The war was initially viewed as a fight to contain communism (see containment, Truman Doctrine, and Domino Theory), but, as more Americans were drafted and news of events such as the Tet Offensive and My Lai massacre leaked out, American sentiment turned against the war . U.S. President Richard Nixon was elected partially on claims of a "secret plan" to stop the war . This Nixon Doctrine involved a gradual pullout of American forces; South Vietnamese units were supposed to replace them, backed up by American air power . Unfortunately, the plan went awry, and the war spilled into neighboring Cambodia while South Vietnamese forces were pushed further back . Eventually, the U.S. and North Vietnam signed the Paris Peace Accords, ending U.S. involvement in the war . With the threat of U.S. retaliation gone, the North proceeded to violate the ceasefire and invaded the South with full military force . Saigon was captured on April 30, 1975, and Vietnam was unified under Communist rule a year later, effectively bringing an end to one of the most unpopular wars of all time . </P> <P> The Cuban Missile Crisis illustrates just how close to the brink of nuclear war the world came during the Cold War . Cuba, under Fidel Castro's socialist government, had formed close ties with the Soviet Union . This was obviously disquieting to the United States, given Cuba's proximity . When Lockheed U-2 spy plane flights over the island revealed that Soviet missile launchers were being installed, U.S. President John F. Kennedy instituted a naval blockade and publicly confronted the Soviet Union . After a tense week, the Soviet Union backed down and ordered the launchers removed, not wanting to risk igniting a new world war . </P> <P> With Cold War tensions running high, the Soviet Union and United States took their rivalry to the stars in 1957 with the Soviet launch of Sputnik . A "space race" between the two powers followed . Although the USSR reached several important milestones, such as the first craft on the Moon (Luna 2) and the first human in space (Yuri Gagarin), the U.S. allegedly pulled ahead eventually with its Mercury, Gemini, and Apollo programs, which culminated in Apollo 11's manned landing on the moon . Five more manned landings followed (Apollo 13 was forced to abort its mission). Nevertheless, despite its successes the U.S. space program could not match many major achievements of the Soviet space program, such as unmanned rover - based space exploration and image and video transfer from the surface of another planet, until the early 21st century . </P>

In which order did america’s twentieth century wars occur