Kim Jong-un, the leader of North Korea, plans to travel to Russia this month to meet with President Vladimir V. Putin to discuss the possibility of supplying Russia with more weaponry for its war in Ukraine and other military cooperation, according to American and allied officials. In a rare foray from his country, Mr. Kim would travel from Pyongyang, North Korea’s capital, probably by armored train, to Vladivostok, on the Pacific Coast of Russia, where he would meet with Mr. Putin, the officials said. Mr. Kim could possibly go to Moscow, though that is not certain. Mr. Putin wants Mr....