Australian Labor Party split of 1955

The Australian Labor Party split of 1955 was a split within the Australian Labor Party along sectarian and ideological lines in the mid-1950s. With the exception of the consequences of The Petrov Affair, the Liberal/Country Coalition had little or no influence on the split; it was essentially an internal conflict between elements of the Australian Labor Party. Key players in the split were the federal opposition leader H. V. "Doc" Evatt and B. A. Santamaria, the dominant force behind the "Catholic Social Studies Movement" or "the Movement".

Evatt denounced the influence of Santamaria's Movement on 5 October 1954, about 4 months after the 1954 federal election. The Victorian ALP state executive was officially dissolved, but both factions sent delegates to the 1955 Labor Party conference in Hobart. Movement delegates were excluded from the conference. They withdrew from the Labor party, going on to form the Australian Labor Party (Anti-Communist) which in 1957 became the Democratic Labor Party. The split then moved from federal level to states, predominantly Victoria and Queensland.

Historians, journalists, and political scientists have observed that the split was not a single event but a process that occurred over the early 1950s in state and federal Labor parties. The conservative Catholic and staunchly anti-Labor Democratic Labor Party has used Australia's full-preference instant-runoff voting system to direct its preferences to benefit the Coalition two-party-preferred vote and was successful until 1972 in preventing the election of an Australian Labor Party federal government.

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