How does collaboration with an ally influence public support for overseas counterinsurgency (COIN) operations? Recognizing the pivotal role of public opinion in foreign policy decisions, this study employs survey experiments in the United States to investigate whether collaboration with an external actor enhances public backing for COIN operations. I argue that working with a partner persuades the public because the costs are shared, the success is more likely, the people see the operation as necessary, and the threat is perceived as more imminent. While existing research often examines the impact of multilateral alliances, particularly within international organizations like the UN or NATO, my focus is on specific types, such as local, regional, and traditional Western allies given the increasing hostility in the American public towards those organizations. I find that collaboration with external actors does not influence Americans' support for COIN operations on average. Nevertheless, further analyses show that Republicans and Democrats have contrasting preferences regarding collaborating with Western allies. By exploring the potential of collaborations beyond formal international bodies, my research contributes to the growing body of research examining how leaders can garner public support for war-related matters.