Contemporary abolitionists frequently turn to anti-slavery abolitionism for inspiration. This chapter argues that they should look to the more ambivalent legacy of anti-prostitution abolitionism in order to learn from earlier mistakes. It examines the League of Nation’s investigations into global sex trafficking in the interwar period to explore what the study of anti-trafficking abolitionism can reveal to contemporary activists and policymakers. It suggests that anti-prostitution abolitionist campaigns of the 1920s and 1930s warn of the oversized influence of philanthropists on the construction of global agendas; the dangers of the Global North shaping the terms of international knowledge production that become implicated with racialized understandings of trafficking; the (un)intended outcomes of stricter border control and empowered carceral systems that target women assumed to be migratory prostitutes.