U.S.-South Korea Joint Military Exercises: Why North Korea Gets Upset Expert: “The North Koreans train much heavier than we do … From December through March, they train every one of their organizations. They start at the lowest level—the soldier—and work up through the squad and platoon and stuff. And then by March, they’re at the zenith of their offensive readiness. That’s provocative.” It’s often reported in the media that countries are performing “joint military exercises.” Such exercises are happening this week, during the visit to Asia by the U.S. secretary of state and secretary of defense, which prompted a loud rebuke from Kim Yo-jong, the sister of North Korea leader Kim Jong-un. During the talks in 2019 between then-President Donald Trump and Kim, Trump reportedly agreed to end the exercises with South Korea, after previously calling them a waste of money.