[9] Although long-standing ideological differences and factional rivalries played a key role, the proximate cause of the split was internal disagreements over how to conduct the ongoing Anpo protests against revision of the Treaty of Mutual Cooperation and Security Between the United States and Japan, known as Anpo in Japanese, and whether or not to cooperate with the Communist Party of Japan in doing so.

[9] Declassified United States government documents later revealed that covert CIA funding had also helped encourage the founding of this breakaway party.

After Minsha Youth was dissolved, some of its former members and independent social democrats formed Young Socialists, a new youth organisation which retained full membership in IUSY; however, it was finally dissolved on 8 March 2008 without any successor organisation and abandoned its IUSY membership.

The DSP was rated "moderate",[14][15][16] "moderate social-democratic",[17][2] "centrist"[4][5][6] and "centre-left"[7] by Japanese political standards at the time, but at the same time it was also regarded as a "conservative"[3][8][18] political party.

It derived much of its financial and organisational support from the Domei private-sector labour confederation, but unlike other social-democratic political parties in Japan, the party was not hostile to accepting neoliberal policies[19] Due to the DSP's syncretic political position, the party's ideology is often referred to as right-wing social democracy (右派社会民主主義).