Why do states join US-led military coalitions? The compulsion of the coalition's missions and legitimacy

Why do states join US-led military coalitions? The war/dispute-diffusion literature suggests that opportunity and willingness are crucial determinants of coalition participation (Siverson snd Starr.1990, 1991). A state joins a coalition if it has a strong interest in war and enough capability to send armed forces abroad. Alliance studies connect coalition participation problems with the reliability of allied countries (Leeds, 2003 Gartzke and Gleditsch, 2004). These studies seem to provide a fairly good picture on the question; however, they are not free of problems. In particular, they study only coalitions for interstate war and militarized disputes but ignore coalitions for other purposes. Coalitions can be formed for military operations other than war (Kober, 2002). There are coalitions for humanitarian intervention, peacekeeping, and even for the evacuation of noncombatants. This article shows how difference in operation-types and collective legitimacy affect the decision of a state to participate in US-led coalitions. A coalition with United Nations' authorization may appear to be a legitimate international 'police' act and attract more partner states. A coalition for intervention into domestic affairs may be less attractive to possible participants because of the violation of the noninterference norm of international law. Statistical analysis on United States coalition partners from 1950 to 1999 suggests that how and for what purposes coalitions are formed cannot be overlooked. Coalition participation is not fully explained by the existing perspectives found in war/dispute-diffusion literature and alliance studies, and there is a need to invok 'the compulsion of the coalition's missions and legitimacy'.