New Delhi, Sept. 6 -- Kim Jong Un put on a command performance this week at a gathering of some two dozen world leaders in China, striding with confidence and a broad grin across one of the biggest international stages of his 14-year career as North Korea's leader.

As Kim returns home Friday, his time in Beijing marks a stunning transformation from his first tentative, violent years in power, when some analysts suggested the inexperienced young leader would struggle to survive threats to his rule.

Serious diplomacy with a large group of leaders was unimaginable.

But in Beijing, Kim looked like the leader his propaganda services have constantly sought to portray: an important - crucial, even - player in world affairs, entirely at home w...