The United States flew a long-range bomber in a trilateral drill with South Korea and Japan on Sunday in response to North Korea’s recent test-firing of a new intercontinental ballistic missile designed to strike the US mainland, South Korea’s military said. North Korea on Thursday tested the newly developed Hwasong-19 ICBM, which flew higher and stayed in the air longer than any other missile it has fired. North Korean leader Kim Jong Un called it “an appropriate military action” to cope with external security threats posed by its rivals. On Sunday, the US flew the B-1B bomber to train with S…