“Enforcing Transnational White Solidarity” examines the struggle over Asian migration and labor trafficking in the Pacific Northwest, showing how it gave rise to a new emphasis on border policing and surveillance on the North American continent in the late nineteenth and early twentieth centuries. The transnational circulation of Asian merchants, contract laborers, and smugglers integrated disparate points in the Pacific into a complex web of networks, with their myriad of movements traversing multiple and intersecting imperial and national spaces, linking the North American West to Asia and the South Pacific. These ever thickening global connections kindled a countermovement to solidify national borders among Anglo-American settler societies in the Pacific Northwest, who together elaborated new forms of sovereignty in an attempt to exert control over the mobility of Asian migrants around the Pacific and across landed borders in North America, even as they integrated the Pacific Northwest into a larger world. This article reveals how this double movement transformed the U.S.-Canadian boundary from an imaginary abstraction to a social reality on the North American Pacific Rim. It argues that efforts at Asiatic exclusion codified immigration and boundary controls as rightful prerogatives of the nation-state, which in turn, reconstructed racial and national borders through its practical enforcement in Canada and the United States. By relocating the historical origins of the border from the southern to the northern boundary, the article demonstrates that this struggle was transnational in scope, involving contests over Asian migration that extended across the Pacific world. In doing so, it highlights the contested and contingent process of consolidating the territorial state, and considers the multiple and overlapping sites—local, national, and the imperial—that shaped and defined its historical development.