The Japan Socialist Party (JSP) was a democratic socialist political party in Japan which was active from 1945 to 1996. It was the successor of the pre-World War II Shakai Taishuto and other socialist parties, and it was briefly in power from 1947 to 1948 under Prime Minister Tetsu Katayama. From 1951 to 1955, the party was divided between the Marxist Leftist Socialist Party and the social democratic Rightist Socialist Party, but the JSP maintained a third of the seats in the National Diet and were thus able to prevent the dominant conservative LDP party from amending the Japanese constitution. During the late 1980s and 1990s, the JSP was met with record levels of success under Takako Doi, but the establishment of new conservative parties during the 1990s led to the JSP's support declining. In 1996, the JSP was succeeded by the minor Social Democratic Party.