Lesser of two evils principle
The lesser of two evils principle was a Cold War-era foreign policy principle used by the United States and to a lesser extent, several other countries. The principle dealt with third-world dictators and what the US' policy for dealing with them should be. It is related to the Kirkpatrick Doctrine of Jeane Kirkpatrick.
The United States had long held support for democracy to be one of their stated cornerstones of US foreign policy. However, following the Second World War democracy was still a fairly uncommon governmental method, and dictatorships continued to hold power over many of the world's most stragetically important reigons. The United States would thus form alliances with certain dictators, believing them to be the closest thing their respective nations had to a legitimate government. Many of these dictators were pro-capitalist, and thus consistent with at least some of the US' ideological goals.
Conflicts over dictatorships began to occur when the Soviet Union began to support Communist revolutions and guerilla uprisings against established dictatorial regimes. In many cases these movements succeeded, and replaced an American ally dictator with an anti-American and pro-Soviet one. This struggle posed a question- if the end result was destined to be a dictatorship, should not the US try to align itself with the dictator who will best serve American interests and oppose the Soviets? This is what became known as the "lesser of two evils" principle.
Probably the best example of this principle in action was the political stuggle behind the Vietnam War. Ngo Dinh Diem was the dictatorial ruler of South Vietnam during the inital stages of the war. Though his regime was brutal, he was also an anti-Communist who was determined to fight the expansions of the Communist North. Ho Chi Minh was the dictatorial ruler of North Vietnam, backed by the Soviets, and an ardently patriotic Marxist who wanted to see a united, self-governing, communist Vietnam. The United States thus supported the regime of Diem and his successors during the war, believing that he was the "lesser of two evils."
Application in other nations
Many other countries, including the Soviet Union, also had their own "lesser of two evils" policy.
Earlier, during World War II, the Western Allies justified their support for the tyrannical Communist regime of Stalin under a lesser-of-two-evils principle. Winston Churchill said: "If Hitler were to invade Hell, I would at least make a favourable reference to the Devil in the House of Commons."
The decision of the leadership of the People's Republic of China to seek rapprochement with the United States in the 1970s can be seen as an application of the "lesser of two evils doctrine," with the United States being deemed a lesser threat than the Soviet Union.