Seven words, spoken almost in passing on a recent afternoon in Srinagar, have set off a diplomatic tremor across South Asia. “This is an important part of India,” Sergio Gor told reporters on August 19, during the first visit by a US ambassador to Indian-administered Jammu and Kashmir in six years. Within hours, Pakistan had summoned the top American diplomat in Islamabad, Natalie Baker, to deliver a formal protest. Kashmir, a disputed Himalayan region claimed in full by both India and Pakistan,...