This book is about the British campaigns against the new slaveries of European imperialism in Africa in the late nineteenth and early twentieth centuries. It illuminates a pivotal period in British anti-slavery protest after the legendary age of emancipation, bridging the gap in historical scholarship between the Victorian era of abolition and the rise of labor law and human rights protest under international government. It begins by outlining the development of the ideologies of British humanitarianism and empire through the Victorian era, then examines three interrelated campaigns against new slaveries in the Congo Free State and Britain's Transvaal Colony in South Africa and on the islands of Sao Tome and Principe. These case studies illustrate how advocates of evalngelical philanthropy and human rights influenced British responses to the new slaveries and how the ensuing debates relected divisive class and partisan politics, as well as the calculations of big business. Finally, the book demonstrates that Britain's humanitarian responses to the new slaveries in Africa played a central role in establishing the foundations of twentieth-century international government and labor law as a "sacred trust" under the League of Nations.