Cable Empires uncovers the hidden communications infrastructure that helped shape the international legal order. From submarine telegraph cables to the fiber-optic systems that underpin today's digital economy, global communication networks linked distant territories, reshaped knowledge, and transformed governance across empires, markets, and states. Cable networks unsettled conventional understandings of jurisdiction and sovereignty, while enabling new forms of political and economic power beyond territorial borders. At the same time, their construction and operation depended on Indigenous labor, resource extraction, corporate and state capital, territorial access, and international law. Bridging international law, history, and science and technology studies, Cable Empires offers a new account of how communications infrastructure and technology were intertwined with the development of the international legal order. In an era marked by struggles over digital sovereignty and geopolitical rivalry, it offers insight into the material and historical foundations of contemporary power and the legal arrangements that sustain them.