Karl Kautsky’s Ultra-Imperialism shaped his understanding of European colonialism and Great Power competition. In the early twentieth century, Kautsky argued that explanations for world disorder stemmed from what liberal and bourgeois politics avoided— harmonizing class relations and making their states more democratic. He characterized that the capitalist bourgeois approach to world order would be via international cartels and monopolies. They were ideologically and economically unable to offer alternatives routes to peace. He predicted that in an ultra-imperialist world order, the great powers would deepen their exploitation of the world’s resources and working class labour. In situating Kautsky in his context, this article connects his socialist republicanism with his aspirations for a Society of Nations, and finds that he imitated form August Ludwig von Rochau’s Realpolitik, in that he delineated a political strategy to build a socialist world order through his political activism. This paper then calls into view that analytical discussions of Great Power competition have to consider the politics within states. Ultra-Imperialism has hitherto been underexplored but it provides a potential route to understand the causes and character of the emerging polycentric world order.