BEIJING — The young leader of North Korea likes to present himself as a modern man projecting his isolated country onto the world stage.

But for his meeting with President Trump in Vietnam this week, Kim Jong-un is traveling south through China in an armored train — not even a high-speed one — and then planning to drive the last leg to Hanoi, the Vietnamese capital. The journey is expected to take as long as two days from the starting point in Pyongyang, the capital of North Korea, instead of a few hours by plane.

His unusual itinerary can be explained by geopolitics, the rickety state of North Korean aircraft and a bit of history.

Mr. Kim, who left the railway station in Pyongyang on Saturday, appears to be indulging China by taking such a protracted trip. His khaki-green train will take him past glistening cities and productive countryside that show off the country’s four decades of blazing economic growth.