BEIJING — In late December, a group of teenagers from North Korea traveled to the Chinese city of Kunming to play in an obscure under-15 soccer tournament. On the field, under a wintry sun, they faced teams from China and South Korea. Off the field, there was an unusual spectator: Choi Moon-soon, the governor of the province in South Korea hosting the Winter Olympics.

Mr. Choi had flown more than 1,000 miles to meet the North Korean officials accompanying the young players — and to make the case for North Korea to attend the Olympics. “We were looking for any contact with North Korea, and the youth soccer teams were the only inter-Korean exchange still going on,” he later recalled.

Even before Mr. Choi returned to South Korea, his government sent another signal: In a television interview, the South’s president, Moon Jae-in, said he favored postponing annual joint military exercises with the United States — an unmistakable overture to North Korea’s leader, Kim Jong-un, who had long condemned the exercises.

Mr. Kim soon reciprocated, declaring at the start of the year that he was sending his athletes to the Olympics. There, they will march in the opening ceremony on Friday under a unified Korean flag with the South Koreans — a historic moment for the divided Korean Peninsula.