The United States and South Korea have begun four days of joint military exercises in the waters off the Korean coast, in an effort to deter North Korea from launching further attacks across its border with the South. An American nuclear-powered aircraft carrier is leading the drill, which comes just days after North Korean forces shelled the South Korean island of Yeonpyeong, killing two marines and two civilians. North Korea’s state-run media has criticized the drills, warning the two Koreas are on ‘the brink of war.’