Bulgaria–United States relations to work. Bulgaria became a member of the Warsaw Pact on May 14, 1955. Though no Soviet troops were stationed on Bulgarian soil, in 1968, Zhivkov sent a Bulgarian division to join Polish, Hungarian and Soviet troops to crush a popular uprising in Prague. In 1978, the Bulgarian secret police were implicated in the assassination in London of Georgi Markov, a Bulgarian dissident who was a correspondent for the BBC World Service, Deutsche Welle radio and the U.S. sponsored Radio Free Europe. Markov was assassinated with a poisoned umbrella on September 7, Zhivkov's birthday. The rise of democratic movements across
People's Republic of Bulgaria his leg with the tip of an umbrella. Markov died shortly afterwards of ricin poisoning. He was the victim of the Bulgarian secret service, as confirmed by KGB documents revealing that they had jointly planned the operation with Bulgaria. The Bulgarian People's Army sided with the Soviet Union and the Afghan communists during the Soviet–Afghan War in Afghanistan fighting the jihadist guerrillas from 1982 until its withdrawal in 1989. By the 1980s, the conservatives controlled the government. Some social and cultural liberalization and progress was led by Lyudmila Zhivkova, Todor's daughter, who became a source of strong disapproval and annoyance