The Socialist Party of Japan (SPJ) is a political party founded in 1945, emerging from the post-World War II political landscape. It aimed to promote socialism and advocate for workers' rights, social justice, and democratic governance. The party played a significant role in Japanese politics during the mid-20th century, particularly in the opposition against the ruling conservative parties. Over the years, the SPJ has faced challenges, including declining membership and electoral support. In 1996, it merged with the New Socialist Party to form the Social Democratic Party of Japan, which continues to represent socialist ideals in contemporary Japanese politics.