This chapter interrogates the widely accepted idea that international law was diffused from the European centre to the colonial periphery through economic and political processes. The chapter examines legal principles of colonial governance and shows how those principles are elevated to principles of global governance after the end of the world wars. It maps the trajectory of certain founding concepts in international law from colonial rule to the present. Viewed from the standpoint of colonial histories, the present period based on sovereign equality of states is not less imperial than past empires. The ‘diffusion thesis’ abstracts legal consciousness from social consciousness and removes the anti-colonial resistances from accounts of histories of international law. Besides, by dating the histories of international law from the nineteenth century, the diffusion thesis leaves out the role of trading corporations in the development of international law. By abstracting legal relations from the materiality of social relations and side-stepping more fundamental questions about the nature of so-called ‘development’, the diffusion thesis obscures the ways in which the economic power of corporations and the political powers of capitalist states coalesce in imperial governance during different periods of capitalism and (neo) colonialism.