New York Times writes that the first time Shinzo Abe, Japan's prime minister, met President Xi Jinping of China, the body language told the story. Mr. Xi looked dour and stiff, turning away from Mr. Abe with pursed lips, as if someone had forced him into it after months of escalating tensions between their two nations. In the years since, relations have improved but the two leaders have always kept at a distance. This past weekend, they met again on the sidelines of a regional summit meeting in Vietnam. This time, they shook hands and Mr. Xi flashed a grin. It was a sign, the Japanese news media suggested, of a potentially momentous shift in the region, with two longtime adversaries drawing closer as the United States under President Trump has created unease among allies about the role the United States will take in the region.To compensate, Japan and China are inching toward a possible reconciliation as they recognize the altered dynamics around the Pacific Rim...In gesturing toward a new friendliness, Japan is motivated in part by the recognition that as the United States retreats, it needs stronger trade with China. Having watched Mr. Trump heap praise on Mr. Xi in Beijing last week, Japan is also propelled by fear that the United States may develop a closer rapport with China that would exclude Japan. And as China seeks to strengthen its power, it realizes it may have more success exerting authority in the region with Japan as less of a rival. At the same time, Mr. Trump's visit showed China that the United States is unlikely to get in its way, allowing a more confident Mr. Xi to be more generous toward Japan.