SEOUL, Aug. 18 (UPI) -- The United States and South Korea kicked off their annual summertime joint military exercise on Monday, amid efforts by Seoul to improve relations with North Korea . The 11-day Ulchi Freedom Shield exercise, which runs through Aug. 28, includes live field maneuvers, computer simulation-based command post exercises and related civil defense drills. Some 21,000 troops will be mobilized, including 18,000 South Korean personnel. Pyongyang, which routinely condemns the allies'