In counterinsurgency wars with large-scale foreign military interventions, under what conditions do in-country allies comply with the demands of foreign intervening forces and under what conditions do allies dismiss foreign demands? By examining thousands of primary source documents drawn from foreign interventions in Vietnam, Afghanistan (U.S.S.R.), Sri Lanka, Afghanistan (U.S.), and Iraq, the study uses both qualitative and quantitative methods to analyze 460 specific requests from foreign allies to their in-country counterinsurgency partners, measuring conditions affecting in-country allied compliance with (or defiance of) foreign requests. Revisiting definitions of "power" in international relations and moving beyond underspecified explanations of alliance politics, this study theorizes that certain structures inherent in this type of counterinsurgency partnership influence the behavior of in-country allies. Specifically, the study argues that five factors influence the likelihood of in-country compliance with foreign allied demands, including: 1) the potential unilateral ability of intervening forces to implement the requested policy; 2) the alignment of allied preferences over the policy; 3) the capacity of the host government; 4) wartime complications; and 5) the presence of an acute enemy threat. These variables interact with each other to produce a complex set of incentives for allied cooperation or defiance. In particular, the study argues that whether or not allied interests converge or diverge over a proposed policy interacts with the unilateral ability of intervening forces to implement the policy. For example, if allied preferences converge and the foreign ally can implement the request unilaterally, the host ally has an incentive to free-ride and is unlikely to comply. Conversely, if allied interests diverge and the foreign ally can implement the request unilaterally, the in-country regime has an incentive to participate in order to avoid being undermined by its ally acting unilaterally. Overall, the study found remarkable consistency across this subset of wars, with approximately 1/3 of foreign requests complied with, 1/3 complied with in part, and 1/3 left unfulfilled.