The U.S. has begun deploying the Terminal High Altitude Aerial Defense - THAAD - an anti-missile system meant to defend South Korea against attacks from the North. The first components arrived in South Korea last week.
U.S. Forces Korea
President Trump and Defense Secretary James Mattis speak on Inauguration Day. Mattis travels to South Korea and Japan this week in the administration's first major foreign trip.
Pablo Martinez Monsivais/AP