The first quarter of 2022 has been a time of testing on the Korean Peninsula. In North Korea, the communist regime has been conducting a spate of missile technology trials. Two particularly ominous tests on Feb. 26 and March 4 appear to have involved components that could later be used in an intercontinental ballistic missile capable of reaching the United States. Given that this could foreshadow an end to Pyongyang’s self-imposed ban on long-range missile testing, the Biden administration was right to call North Korea’s behavior a “serious escalation” and to announce that the U.S. Indo-Pacific Command would step up surveillance and missile defense force readiness.

Meanwhile, south of the 38th parallel, the Republic of Korea was conducting a different kind of test — of its democratic political system, in the form of a very close presidential election. On the whole, South Korea’s 35-year-old democracy passed with flying colors. Though voters were deeply polarized along left-right lines, and the major candidates ran almost exclusively negative campaigns, the voting was free and fair. The victor, conservative Yoon Suk-yeol, got only 263,000 more votes than progressive rival Lee Jae-myung, but the latter quickly and graciously conceded his defeat. The stage is set for something that has never even come close to happening in the North — a peaceful transfer of power. And the closeness of the race, coupled with continued opposition control of Congress, may restrain Mr. Yoon’s ability to enact his more questionable campaign promises, such as a pledge to abolish the country’s Ministry of Gender Equality and Family.

Perhaps most important for the United States, Mr. Yoon promises to end the efforts of his predecessor, Moon Jae-in, to steer South Korea’s foreign policy on a more conciliatory path with respect to China and its client, North Korea, while distancing Seoul from the United States. The Moon government consciously played down North Korea’s human rights violations and balked at installing additional U.S. theater missile defense systems. The purpose was to preserve commercial relations with China while gradually inducing North Korea to modify its behavior. Seoul wound up with little to show for these overtures, as the North’s missile tests and China’s backing for Pyongyang, despite its nuclear weapons programs, demonstrate.

Mr. Yoon proposes instead to make South Korea into a “global pivotal state,” with an active international role commensurate to its economic strength and liberal-democratic values. As part of that, he advocated “a deeper alliance with Washington,” which should be “the central axis of Seoul’s foreign policy.” As well, Mr. Yoon wants South Korea to mend fences with Japan, a perennial sore spot left over from the latter’s occupation of Korea before and during World War II. If it goes according to plan, Mr. Yoon’s policy could bolster democratic unity across the Indo-Pacific and help prevent China from using North Korea as a means to weaken and distract what should be a united front of countries deterring it from aggression against Taiwan.