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
Umbrella (newsletter) Umbrella (newsletter) Umbrella was an art newsletter or informal magazine that ran for three decades, from 1978 to 2008. Its focus was on artist's books and related media, and it has been credited as an important factor in the emergence and visibility of artist's books from Southern California. "Umbrella" was founded by curator Judith Hoffberg in 1978, and she remained its editor for the duration of its existence. Appearing irregularly, between 2 and 6 times a year, "Umbrella" focused on artist's books and related printed matter such as mail art, Xerox art, and photobooks. Hoffberg had a particular interest in