This article seeks to explain the difference in alliance relations by closely examining the processes, policies, and problems involved in triangular diplomacy. In a tight two-against-one relationship, the argument is that adversarial engagement creates an incentive for intraalliance tensions. Yet, conflict between the two allies can be mediated by two factors: the presence of reassurance from the ally and the absence of an alternative security provider. Two comparative case studies are used to probe the plausibility of the hypothesis concerning triangular dynamics. The first case involves the Seoul-Moscow-Pyongyang triangle and the second the Seoul-Being-Pyongyang triangle-both during the period from 1988 to 1994. As a result of South Korea-USSR rapprochement, Pyongyang Moscow relations deteriorated rapidly; yet, despite South Korea-China normalization, the politico-military cohesion in Pyongyang-Beijing relations remained largely unharmed. The difference in North Korea’s response can be attributed to China’s reassurance and North Korea’s lack of alternative ally.