This chapter elucidates first the undercurrent phenomenon in social movements generally and its application to Japan, providing a long-term perspective on the 1960 events. Having outlined the formation and gradual polarization of political parties – including their main bones of contention – the overall attributes of the social movements during 1945–58 are spelled out, stressing their notable emergence already in the early post-surrender years, despite Japan’s utterly wretched conditions. We then examine the dynamics of specific social movements, clustering around the themes of defending peace and democracy, widely perceived as threatened by the policy pursuits of successive conservative governments. Concrete cases of protracted, cumulative grassroots activism conclude the discussion of historically evolving undercurrents.