In 1916 the Labor Prime Minister, Billy Hughes, decided that conscription was necessary if the strength of Australia's military forces at the front was to be maintained. The Labor Party, Irish Australians, Catholics and the trade unions (heavily overlapping categories) were bitterly opposed to conscription, and Hughes and his followers were expelled from the party when they refused to back down. In 1916 and again in 1917 the voters rejected conscription in national plebiscites. (See History of Australian Conscription) Hughes united with the Liberals to form the Nationalist Party, and remained in office until 1923, when he was succeeded by Stanley Bruce. Labor remained weak and divided through the 1920s. The new Country Party took many country voters away from Labor, and in 1923 the Country Party formed a coalition government with the Nationalists.