The leaders of the world's 20 largest economies meet in Seoul, South Korea, Wednesday with many expecting a fight over currencies to loom large. President Barack Obama is in town, hoping to assure the world that the American economy is secure. Countries have pledged not to use their currencies as trade weapons. Yet the U.S. Federal Reserve's plan to buy $600 billion in bonds has angered many trading allies. Countries say the money will flood their markets, driving up the value of their currencies, eventually destabilizing their financial systems.