The United States warned Saturday that China's military claim to airspace over a disputed island chain creates the risk of "misunderstanding and miscalculation." The creation of an "Air Defense Identification Zone" by China, which its top defense official described as an early-warning system, comes amid rising tensions between China and Japan over claims to the islands that are believed to have large oil reserves. "This unilateral action constitutes an attempt to change the status quo in the East China Sea. Escalatory action will only increase tensions in the region and create risks of an incident," U.S. Secretary of State John...