An unavoidable fact of modern geopolitics is this: China and the United States, the world’s two largest economic and military powers, are separated by approximately 8,000 miles of ocean. This means that dynamics at sea – especially in the Pacific, but increasingly now in the Indian, Arctic, and Atlantic Oceans – will heavily shape tensions and transactions between the United States, China, and other major states. The Brookings Seas and Strategy series explores the complex questions and problems that all states will confront as the future increasingly becomes defined by the use of power on — and under — the world’s oceans.