In the early 1900s, the US government experimented with what they saw as a progressive style of influence in the Dominican Republic. While the Roosevelt and Taft administrations sought alternatives to armed intervention, US officers serving as diplomats pushed for more direct military control, through projects such as the creation of a US-officered frontier guard. Established in 1905 to police revenue along the Dominican-Haitian border, this unique organization had neither precedent nor sanction in international law, but it demonstrated the makeshift Caribbean policy of an expanding United States — and how this expansion gradually militarized diplomacy. Paternalist discourse and rapid economic change perpetuated internal strife, eventually contributing to bloody civil war and outright US military occupation (1916–1924). This article explores the development of the frontier guard and interventionism, focusing on the roles of Dominican economic and political change and contemporary US expansionist ideology, with its goal of exporting US-style democratic institutions.