This study considers the contribution of climate change as an important causative factor in later Medieval Japanese history. The peasant ikki civil disturbances from 1459–1467 are closely concurrent with the Little Ice Age, when colder temperatures and uneven precipitation contributed to widespread famine. In historiography, these years mark the end of Japan's Middle Ages and beginning of the Warring States Period. Referencing contemporary written accounts, a retrospective methodology is used here to examine how social conflicts emerged during natural disasters by first focusing on organized resistance actions as an outcome, then clarifying conditions for these actions, and finally identifying how these conditions could have been triggered by climate disruption. “Climate causality” in this case may be most accurately expressed as a moderation model, whereby climate disruption exacerbated and accelerated latent socioeconomic discontent among peasants and regional elites’ designs for autonomy. Desires for tokusei, or “moral governance”, may have also motivated resistance to paying taxes during times of poor harvests. Due to its relative isolation Medieval Japan lacked the confounding factors of religious strife and foreign wars, and therefore it presents a plausibly generalizable illustration of sociopolitical impacts from climate change.

Keywords: Medieval Japan, Little Ice Age, Famine, Peasant Unrest, Sociopolitical Conflict, Causation