By 1909, Australia had evolved a two-party system at the federal level, with the conservative Commonwealth Liberal Party and the progressive Australian Labor Party having both alternately won power via general election. This system was upset in November 1916, when the Labor party split over the issue of conscription; Prime Minister Billy Hughes and his pro-conscription supporters left the Labor party and formed a minority government as the "National Labor Party", before merging with the Liberals in February 1917 to form the Nationalist Party with Hughes as their leader.