1951. While both attempts were unsuccessful, further international events such as the defection of minor Soviet Embassy official Vladimir Petrov, added to a sense of impending threat that politically favoured Menzies' Liberal-CP government, as the Labor Party split over concerns about the influence of the Communist Party on the trade union movement. The tensions led to another bitter split and the emergence of the breakaway Democratic Labor Party (DLP). The DLP remained an influential political force, often holding the balance of power in the Senate, until 1974. Its preferences supported the Liberal and Country Party. The Labor party was led by H.V. Evatt after Chifley's death in 1951. Evatt had served as President of the United Nations General Assembly during 1948–49 and helped draft the United Nations Universal Declaration of Human Rights (1948). Evatt retired in 1960 amid signs of mental ill-health, and Arthur Calwell succeeded him as leader, with a young Gough Whitlam as his deputy. Menzies presided during a period of sustained economic boom and the beginnings of sweeping social change, which included youth culture and its rock and roll music and, in the late 1950s, the arrival of television broadcasting. In 1958, Australian country music singer Slim Dusty, who would become the musical embodiment of rural Australia, had Australia's first international music chart hit with his bush ballad "Pub With No Beer", while rock and roller Johnny O'Keefe's "Wild One" became the first local recording to reach the national charts, peaking at No. 20. Australian cinema produced little of its own content in the 1950s, but British and Hollywood studios produced a string of successful epics from Australian literature, featuring home grown stars Chips Rafferty and Peter Finch. Menzies remained a staunch supporter of links to the monarchy and Commonwealth of Nations and formalised an alliance with the United States, but also launched post-war trade with Japan, beginning a growth of Australian exports of coal, iron ore and mineral resources that would steadily climb until Japan became Australia's largest trading partner. When Menzies retired in 1965, he was replaced as Liberal leader and Prime Minister by Harold Holt. Holt drowned while swimming at a surf beach in December 1967 and was replaced by John Gorton (1968–1971) and then by William McMahon (1971–1972). Post-war immigration Following World War II, the Chifley Labor government instigated a massive programme of European immigration. In 1945, Minister for Immigration, Arthur Calwell wrote