South Korea’s alliance with the U.S. has strengthened during the Biden presidency. But the country’s economy has fallen victim to the rapid rise in U.S. interest rates, showing how Federal Reserve decisions—and the uncertainty around them—can send ripples around the world. The Fed has embarked on a historic spree of interest-rate rises since early 2022, an attempt to rein in inflation that peaked at 9.1% in the middle of last year.