Since universal suffrage was introduced in 1906, the parliament has been dominated by the Centre Party (former Agrarian Union), the National Coalition Party, and the Social Democrats. These parties have enjoyed approximately equal support, and their combined vote has totalled about 65–80% of all votes. Their lowest common total of MPs, 121, was reached in the 2011 elections. For a few decades after 1944, the Communists were a strong fourth party. Due to the electoral system of proportional representation, and the relative reluctance of voters to switch their support between parties, the relative strengths of the parties have commonly varied only slightly from one election to another. However, there have been some long-term trends, such as the rise and fall of the Communists during the Cold War; the steady decline into insignificance of the Liberals and their predecessors from 1906 to 1980; and the rise of the Green League since 1983.