One of the World’s Strongest Stock Markets Is Starting to Fizzle

Challenges are piling up for South Korea’s once highflying shares.

Seoul has been one of the world’s best-performing big stock markets, with its value topping $1.6 trillion in August, according to data from the World Federation of Exchanges. But it has since been hit by rising interest rates, slowing global growth, a clampdown on household borrowing and concern that memory-chip prices may have peaked. A day-trading boom among individual investors is also fizzling out, reducing a key source of support.