South Korean-related assets slumped after the country's president declared martial law, raising concerns among investors about political instability and unrest. The iShares MSCI Korea ETF fell 5.1 percent in U.S. markets, its biggest one-day drop since Aug. 5. The Korean won fell to its lowest level against the dollar in more than two years. Shares in London-listed Samsung Electronics fell 5 percent. Arup Chatterjee, a strategist at Wells Fargo in New York, said domestic uncertainty in South Kor...