North Korea threatens to pull out of negotiations over South Korea USA military exercises.
Game theory:
Publicly say ok fine; it disappoints us they are taking this stance, but we are committed to these exercises as they have been planned for a long time and provide training and cooperation between allies. Our hope is that in the not too distant future that North Korea can join the USA and South Korea in these exercises, after full denuclearization.
Then in private offer a larger border buffer - like 10 miles.