Humanitarian assistance had long implied the potential of forceful intervention. International responsibility for the protection of human rights and alleviation of human suffering led to the development of international institutions, including the multinational United Nations. The development of international law, from the Geneva conventions to the response to the Holocaust at Nuremberg and the UN Declaration of Universal Rights increasingly reflected the idea that the international community could hold individuals and nations responsible for violations of human rights. Still, what this meant in practice was not clear, and the United Nations was based on respect for national sovereignty. So despite some precedents for humanitarian intervention, the notion that states could intervene in other nations' affairs to protect human rights was not pursued with great vigor until after the Cold War had ended.
Still, Cold War competition led to numerous interventions by the United States and the Soviet Union. Since the Cold War was not only a strategic contest but also an ideological one, each side felt compelled to proclaim the moral basis for their actions, resulting in dubious claims that such interventions as that of the Soviet Union in Hungary in 1956 and Czechoslovakia in 1968, and that of the United States in the Dominican Republic in 1965 and Grenada in 1983, were for humanitarian purposes.
Each side could argue that their political and economic system served humanity's interests, while the other side's represented oppression and the violation of human rights. In such a contest, the definition of "humanitarian intervention" could apply to any superpower attempts to influence a nation to choose sides. By the late 1960s and the 1970s, backlash against this idea spread as some Americans grew frustrated with the nation's foreign policy as a whole, but in particular toward its policy in Southeast Asia. The Vietnam intervention, ostensibly to uphold freedom in the face of communist aggression, alienated Americans as they realized the vast physical, ecological, and human destruction it was causing and as they grew to doubt not necessarily the ability of the United States to defeat the enemy, but its capability to build a nation. By 1979 and 1980, when Vietnam intervened in Cambodia to end the murderous holocaust initiated by Pol Pot and the Khmer Rouge, Americans supported relief efforts for the tens of thousands of Cambodian refugees. On the other hand, they did not support U.S. intervention. The relief efforts were carried out almost entirely by nongovernmental relief agencies, such as Oxfam, a British relief agency, Catholic Relief Services, and the AFSC.
Although there was a revival of support for intervention in the name of humanitarianism during the presidency of Ronald Reagan from 1981 to 1989, it was highly contested. For example, Congress placed curbs on the ability of the Reagan administration to assist the contras in Nicaragua against the leftist Sandinistas, despite administration claims that the Sandinistas were violating the human rights of Miskito Indians. In fact, during the 1980s Reagan faced constant criticism from voluntary humanitarian organizations regarding the administration's policy toward El Salvador. They charged his administration with failing to intervene on behalf of victims of that nation's civil war, choosing instead to support the government despite its failure to curb abuses by the military and right-wing death squads.