From 1948 to 1988, politics in the Republic of Korea were dominated by the executive arm of the government with military backing. Despite this, there were active opposition parties and, with the implementation of the revised 1987 constitution, political parties have had a greater governmental role. In the presidential election of December 1987, the governing Democratic Justice Party (DJP), with Roh Tae Woo as its candidate, won 37% of the vote; the Reunification Democratic Party (RDP), with Kim Young Sam, won 28%; the Peace and Democracy Party (PDP), with Kim Dae Jung, won 27%; and the New Democratic-Republic Party (NDRP), with Kim Jong Pil, won 10%. In a crucial election for the National Assembly in April 1988, the DJP gained only 34% of the popular vote, allowing the opposition parties to control the assembly. This was the first time since 1952 that the government party did not have a majority in, and hence control of, the National Assembly.
In a surprise move in January 1990, the DJP merged with two of the opposition parties, the RDP and the NDRP, to form a new majority party, the Democratic Liberal Party (DLP). In July of that year, two opposition parties, the PDP and the Democratic Party (DP) merged, retaining the name DP. In September 1991, the DP agreed to merge with another opposition party, the New Democratic Party (NDP), then led by the veteran oppositionist, Kim Dae Jung, forming a new DP.
The National Assembly election on 24 March 1992 saw 38.5% of the vote going to the DLP; 29.2% to the DP; 17.3% to the Unification National Party, which later changed its name to the United People's Party (UPP); and 15% to other parties. The actual distribution of seats in the National Assembly shifts as members frequently switch among parties. In the presidential election on 18 December 1992, 41.5% of the vote went to Kim Young Sam of the DLP; 33.8% to Kim Dae Jung of the DP;16.3% to Chung Ju Yung of the UPP; and 8% to candidates of various smaller parties.
Following the 1992 elections, Korea's largest political parties began a period of reorganization. The DLP transformed into the New Korea Party (NKP) while Kim Dae Jung formed a new opposition party, the National Congress for New Politics (NCNP). In the National Assembly election on 11 April 1996, the NKP won 139 seats; the NCNP, 79 seats; the ULD, 50 seats; and the DP, 15 seats. The remaining 16 seats were won by independents. The surprise of the election was the success of the ULD, a conservative party led by former premier Kim Jong Pil.
In the presidential election of 18 December 1997, Kim Dae Jung won 40.3% and Yi Hoe Chang of the Grand National Party (GNP) won 38.7%. In January 2000, Kim reorganized his cabinet; his party, the National Congress for New Politics, assumed a new name: New Millennium Party (NMP).
The 13 April 2000 election involved Kim Dae Jung's New Millennium Party, which captured 115 seats; the former governing party—Grand National Party (formerly the New Korea Party) obtained 133 seats; and a minor party, the United Democratic Liberal Party captured 17 seats. Two seats were held by the Democratic People's Party, one seat was held by the New Korea Party of Hope, and 5 seats went to independents.