After decades of dreaming of a reunified North and South Korea, many South Koreans, young people in particular, now see unification as irrelevant or too costly. This gives urgency to the effort by Park Geun-hye, president of South Korea, to boost domestic support for unification and lay the practical groundwork to make it happen.

The dream is at once quixotic and prudent. On the one hand, it is hard to imagine the North’s leader, Kim Jong-un, voluntarily giving up his family-run dictatorship. On the other, recent Middle East history has shown how quickly borders can shift and regimes can crumble. If that should happen on the Korean Peninsula, leaders there and elsewhere in the region must be prepared to manage a hugely complex and disruptive transition.

As part of her initiative, Ms. Park has named a 50-member commission — including private-sector experts, government officials and the heads of six state-run research institutes — to develop a vision of what a unified Korea might look like, as well as road maps for getting there. In the best case, peaceful reunification would reunite long-separated families, free 24 million North Koreans from dictatorship, enhance regional security and eliminate North Korea’s nuclear threat. Unfortunately, other outcomes seem more likely: the continuation of the present hostile impasse, or, conceivably, the violent collapse of the North Korean regime.

A key player in the peninsula’s future will be China, the North’s chief political patron and the source of its fuel and food imports. Fearful of chaos on its border, China has long refused to exert the kind of pressure that would force radical change in Pyongyang. But China has recently shown more willingness to listen to South Korea on the unification issue, a good sign since Beijing’s cooperation in managing that process would be essential.

Ms. Park is the latest South Korean president to push for unification. But as the differences between the countries harden and younger generations of South Koreans lose interest, she may also be the last.