This book presents Central Europe as a key laboratory for the interwar international order. A new regional order of national states, ushered into being by the dissolution of the multinational Habsburg Empire in 1918, was born alongside a new framework for international governance. The region became the key test case for new international organizations like the League of Nations: problems of border drawing, financial collapse, endemic disease, national minorities, and humanitarian aid emerged as domains where the League’s identity and authority were defined and tested. The predicaments of post-imperial sovereignty, meanwhile, sparked supranational initiatives like international policing and treaties to protect the commercial rights of foreigners. These interactions shaped the successor states as well as institutions of international organization, offering unique insights into the relationship between nationalization and internationalization. Central Europe emerges as a crucible for forms and techniques of supranational governance. With chapters covering international health, international financial oversight, human trafficking, minority rights, scientific networks, technical expertise, passports, commercial treaties, borders and citizenship, and international policing, this book pioneers a regional approach to international order, and explores the origins of today’s global governance in the wake of imperial collapse.