Why do states join wartime coalitions despite the absence of a salient threat or strong ties to the coalition leader? We argue states make unexpectedly high contributions to coalition warfare as a costly signal of their desire for a stronger relationship with the coalition leader. Conventional theories insufficiently explain why states without immediate security interests or strong ties to the lead state over-contribute relative to their capacity. Using newly compiled data on troop contributions to the war in Afghanistan (2001–2014), we find states are most likely to contribute a higher share of their armed forces when their relationship with the US has unrealized alliance potential. States with under-performing alignments leave substantial room for subsequent gains to be had from signaling their commitment to the leading coalition actor. Our finding helps explain why states risk the costs of war—casualties and domestic accountability—by participating in coalition warfare.

尽管没有明显的威胁或与联盟领导人的紧密联系，各州为何仍加入战时联盟？我们认为，各州为联盟战争做出了出乎意料的高贡献，这是他们渴望与联盟领导人建立更牢固关系的代价高昂的信号。传统理论不足以解释为什么没有直接安全利益或与领先国家有紧密联系的国家相对于其能力而言会过度贡献。使用新近收集的有关部队对阿富汗战争的贡献的数据（2001-2014年），我们发现，当与美国的关系没有实现盟军潜力时，各州最有可能贡献更多的武装力量。表现不佳的国家留出了很大的空间，可以通过信号表明他们对主要的联合行动者的承诺而获得随后的收获。