Exit polls project a win for the veteran center-left leader—closing a tumultuous chapter in South Korea's politics, writes Ian Bremmer.

The U.S. ally has been without a permanent leader since late last year, when Yoon Suk Yeol was impeached over his botched declaration of martial law.

Lee Jae-myung was sworn in as South Korea's president on Wednesday, just hours after his victory was certified in a snap election that brought an end to months of political turmoil in the country.