U.S., South Korea begin military exercises as North ends armistice

U.S., South Korea begin military exercises as North ends armistice - CNN.com: "(CNN) -- A new joint military exercise between South Korea and the United States began Monday amid heightened tensions across the region. In a sign of crumbling relations, North Korea refused to answer its hotline with Seoul, South Korea's unification ministry said Monday, according to the Yonhap news agency."