By November 1987, Castro began spending more time on the Angolan Civil War, in which the Marxists had fallen into retreat. Angolan President José Eduardo dos Santos successfully appealed for more Cuban troops, with Castro later admitting that he devoted more time to Angola than to the domestic situation, believing that a victory would lead to the collapse of apartheid. Gorbachev called for a negotiated end to the conflict and in 1988 organized a quadripartite talks between the USSR, U.S., Cuba and South Africa; they agreed that all foreign troops would pull out of Angola. Castro was angered by Gorbachev's approach, believing that he was abandoning the plight of the world's poor in favour of détente. In Eastern Europe, socialist governments fell to capitalist reformers between 1989 and 1991 and many western observers expected the same in Cuba. Increasingly isolated, Cuba improved relations with Manuel Noriega's right-wing government in Panama – despite Castro's personal hatred of Noriega – but it was overthrown in a U.S. invasion in December 1989. In February 1990, Castro's allies in Nicaragua, President Daniel Ortega and the Sandinistas, were defeated by the U.S.-funded National Opposition Union in an election. With the collapse of the Eastern Bloc, the U.S. secured a majority vote for a resolution condemning Cuba's human rights violations at the United Nations Human Rights Commission in Geneva, Switzerland. Cuba asserted that this was a manifestation of U.S. hegemony, and refused to allow an investigative delegation to enter the country.