How did paramilitarism develop into the modern age? The twentieth century has seen forms of paramilitarism ranging from the Freikorps in Germany early on in the century, to the Sudanese Janjaweed militias a century later, and a myriad of armed groups in between. Although these militias all originated under differing conditions and in different societies, their functions, logics, and dynamics demonstrate compelling similarities and instructive differences. This chapter traces the historical context of modern paramilitarism by developing an explicitly global review of these scenarios. The chapter begins with a short overview of paramilitarism in the first half of the twentieth century, before it moves on to the postwar era and looks at the construction of Soviet-led paramilitary infrastructures by the new communist regimes in Eastern Europe, and the US-supported paramilitarization of Latin America in the same period. Paramilitary units also appeared in several European conflicts in the 1990s and committed widespread violence against civilians. Although paramilitarism operated differently in various international political, historical, and ideological contexts in this period, there were both structural and phenomenological similarities between the cases.