After World War II, in November 1945, the major prewar conservative, moderate, and progressives had reorganized and the Japanese Communist Party (JCP) had been legalized. A cabinet under the parliamentary form of government was established under the new constitution that was enforced on 3 May 1947. In the party politics of Japan the "1955 System" or "1955 setup" has played a greater role in overall development of Japan. In this 'system' or 'setup' the reunification of the Japan Socialist Party (JSP), which had split since 1951 and the merger of two conservative parties (Japan Democratic Party and Liberal Party) led to the formation of Liberal Democratic Party (LDP) in November 1955, was called "1955 System or setup", and was dominated by two parties. This resulted later in "one and half party system" since the LDP had about two-times more seats than the opposition party, JSP, in the Diet.
After the formation of 1955 System or setup, the LDP was the dominant political party until 1993. From 1970 to 1983, in every House of Representatives election the opposition parties received more votes than the LDP, and the time was ripe for electoral pacts between all the like-minded opposition parties with the sole purpose of gathering the extra seats in the elections. Nonetheless, oppositions failed to do so, and later development was emerged in the year 1983, elections for the upper house and lower house were held in June and December respectively. The House of Councillors elections went in favor of LDP where it scored 68 seats. The support for the JSP was relatively half to the LDP and it came close to losing its relevance of being the main opposition force. However, the LDP failed to get majority in the upper house for the government formation. Subsequently LDP approached to New Liberal Club (NLC) for alliance and managed 267 seats for majority in house and the JSP improved its tally from the previous elections, achieving 112 seats as the main opposition. This was the first time that the LDP had drawn up a formal policy accord with another party and entered into an actual coalition since the LDP's formation in 1955.
However, the scandals, long awaited reform programs, and factions within the party had led to the downfall of LDP after ruling 38 years in August 1993 and this year is referred as the 'collapse of 1955 System or setup' in Japanese political history. For the short period of time in 1993-1994, LDP was out of power and not represented in government, in 1994-1996 it has returned to the ruling coalition, but under a Socialist Prime Minister Tomiichi Murayama. From 1996-2009, LDP led the government again. In the 2009 elections, LDP lost its plurality in the lower house for the first time. Nevertheless, it returned to dominance in the 2012 elections.
- About Japan Series (1999), Changing Japanese Politics, No. 24, Tokyo: Foreign Press Center.
- Kohno, Masaru. Japan's Postwar Party Politics (1997) excerpt and text search
- Mahendra Prakash (2004), Coalition Experience in Japanese Politics: 1993-2003, New Delhi: JNU.
- Schoppa, Leonard J. The Evolution of Japan's Party System: Politics and Policy in an Era of Institutional Change (2011) excerpt and text search