Integrative complexity, the interaction of conceptual and cognitive rules, is used in processing information. High integrative complexity people evaluate situations and make decisions diversely; low integrative complexity people reason simplistically and dichotomously. We examined the social psychology of South/North Korean relations in their correspondence by an integrative complexity coding process. Time series analysis predicted mean levels of integrative complexity for each half-year period between 1984 and 1997. Analysis showed that South/North Korean relations exert significant influence on integrative complexity levels. We also found a mutual effect of integrative complexity levels in the two. Major coordinative events relate to a decline in integrative complexity in the following half-year period. During South Korean presidential elections, correspondence integrative complexity levels decline in both.