After nine years of conservative rule, a progressive will now occupy the Blue House. Moon Jae-in, the Democratic Party candidate, handily won Tuesday's presidential election in South Korea. His victory will likely result in serious and significant swings in South Korean policy in ways that affect Japan and other nations in the region. There is no time to lose in preparing for those shifts and to build relations with the new government to minimize their impact on Japan.

Moon is a former human rights lawyer and progressive politician who served as chief of staff to the last liberal president, Roh Moo-hyun. He was one of Roh's closest friends; he was in charge of Roh's funeral after he committed suicide and helped settle his affairs. That experience no doubt will have an impact on his presidency and his management of Korean affairs.

Moon won a convincing victory in Tuesday's ballot. He claimed 41 percent of the vote, cleanly besting conservative candidate Hong Joon-pyo with 24 percent of the vote, and the centrist software magnate Ahn Cheol-soo, who claimed 21.4 percent of ballots. With turnout at 77 percent, the highest level in two decades, Moon can claim a genuine mandate.