The expansion of empires in the late nineteenth century prompted leftists to invent a new kind of internationalism targeting what they called “imperialism.” Although there were many ways to combat imperialism, one approach soon came to dominate: the Leninist problematic of the right of nations to self-determination. The ideas that formed the basis of this problematic grew out of highly contingent debates in the twentieth century, but after Lenin’s death in 1924 were codified as the only radical way to change the world on a global scale. It was embraced by millions across the globe, especially by Vietnamese revolutionaries, who soon distinguished themselves as the leading force in the larger anti-colonial struggle in Vietnam. In fact, Vietnam emerged as a kind of test case for the Leninist problematic. It helped Vietnamese revolutionaries score many victories, but the experience of revolution in Vietnam revealed some of Leninism’s core tensions, the most important of which was the contradiction between nation-building on the one hand and universal communist emancipation on the other.