Me, myself, and allies: Understanding the external sources of power

As far back as Thucydides, scholars have hypothesized that power affects the onset of conflict. Despite its importance, power remains a difficult concept to measure, and scholars have primarily relied on material measures that quantify the internal resources available to a state. This concentration on internal sources of power, however, excludes an important power resource available to a state: its external relations. It is reasonable to expect that when a state estimates the power of a potential opponent it looks not only at the internal resources but also at the power of states that would likely join the conflict. In this article, we develop a new measure of external power that explicitly accounts for the external sources of state power. Unlike previous studies that aggregate a state’s expected alliance contributions, our measure is based on the expected contribution of all states, allies and non-allies alike. We conduct a preliminary test of this new measure on dispute onset, and our results provide support for power preponderance over balance of power theories. External power parity contributes to dispute onset rather than deterrence. In addition, we show that examining the combined, rather than individual, effects of external and internal power produces some intriguing results, suggesting that one state’s internal power preponderance can be offset by another state’s preponderance of external power. These results altogether suggest that further studies examining the role of external power can produce fruitful results.