The People's National Movement (PNM), formed in 1956 by Eric Williams, dominated politics in Trinidad and Tobago until 1995. After winning the 1961 elections, the opposition became disorganized. The PNM won all 36 seats in the House of Representatives in an election on 24 May 1972, which the opposition boycotted. When two members of the House of Representatives broke ranks to form a splinter party in June 1972, the PNM monopoly was broken.
In the 1976 elections, the first held under the republican constitution, the PNM won 24 seats, and the new United Labour Front (ULF), a trade unionist party, took 10. The Democratic Action Congress (DAC) elected the two representatives from Tobago.
In the election of 1981, the PNM continued its dominance with 26 seats. The opposition ULF, the DAC, and the Tapia House Movement formed a coalition party, the Trinidad and Tobago National Alliance, and took 10 seats. The Organization for National Reconstruction (ONR), founded in 1980, took 22.3% of the vote but won no seats.
In 1986, the opposition coalition incorporated the ONR and, under the National Alliance for Reconstruction (NAR), took 33 seats to the PNM's three in the December elections. In 1991, the PNM returned to office, winning 21 of 36 seats. The NAR received only two seats, and the United National Congress, under Basdeo Panday, won 13 seats. In the 1992 elections, the NAR won 11 seats and the PNM won one seat.
In 1995, the UNC formed a coalition with the NAR to take control of the House from the PNM. The PNM and UNC each had 17 seats, and the NAR had two seats in the House of Representatives. In the most recent election in 2002, the PNM won 20 seats and the UNC won 16 seats, allowing the PNM to elect its leader Patrick Manning as Prime Minister.
Party membership has been to a large extent based on race and region. The PNM is the party of the blacks. The NAR has been more powerful on the island of Tobago, where it has controlled the local assembly. Whites, Chinese, and other minorities have traditionally been anti-PNM. The UNC is made up of predominantly Indians. The other political parties are the Movement for Social Transformation (MOTION), National Joint Action Committee (NJAC), Republican Party, National Development Party (NDP), and the Movement for Unity and Progress (MUP).