How might great power war arise today? While scholars and policymakers have focused on possible wars arising from accidental or unauthorized clashes or autocratic great powers invading weaker neighbors, this article argues that an alternate pathway--competitive intervention in strategically important states experiencing regime crises--constitutes an alternate significant risk, with clear historical precedent. The political alignment of strategically important states has an outside influence on great power interests, and is something that can quite plausibly be affected over an extended period by external interventions. At the same time, a war that occurred primarily or exclusively within the territory of a secondary state could more plausibly be kept limited--undermining nuclear deterrence--and would not directly conflict with existing norms of territorial integrity. Indeed, I demonstrate that the logic has been a significant source of great power crises and wars throughout history. During the post-WWI period, great power crises occurred more frequently in strategically salient states that were experiencing civil wars or that had experienced irregular regime turnover. In addition, I demonstrate that succession crises arising from the deaths of a monarchs without clear legitimate heirs were an exogenous source of great power war during the monarchic period (1495-1800). I also demonstrate qualitatively that an extended regime crisis in China lay at the heart of the Pacific War in World War II. I conclude the article by discussing implications for the contemporary period, noting in particular the danger of great power war arising from regime instability in either North Korea or Pakistan.