History may look back on this period as an anomaly. Tensions between great powers are again on the rise. In Asia, China is now a legitimate superpower and has been clashing with U.S. allies, such as Japan and the Philippines. It continues to lay claim to a chain of disputed islands in the East China Sea, and it has built 2,000 acres of new islands from sand and coral in the South China Sea, replete with bases and runways. In May, the United States started sending Navy warships to within 12 nautical miles of the islands to assert freedom of passage, and it began mounting surveillance flights over them.