Throughout American political history, the U.S. government has formed alliances with militias, tribes, and rebels. Sometimes, these alliances have been successful, dramatically reshaping the battlefield. But these alliances have also risked creating larger wars in regions where the United States had no real interest. Understanding these alliances-and much of American political history-requires moving beyond our normal focus on traditional diplomats or social elites. Traders, missionaries, former slaves, and low-level government employees drove these alliances. These intermediaries used their relationships across borders to shape security politics, affecting American and thereby world history. Skillfully integrating political science with history and sociology, Eric Grynaviski provides a novel account of who matters and why in international politics. By developing broader views about political agency-how people come to make a difference in world politics-he brings into focus new histories of world politics and how they matter for scholars and the public.