New York — A new level of assertiveness by the United Nations has produced a swift and fortuitous victory over the worst of the marauding militias that have terrorized eastern Democratic Republic of Congo in recent years....

For too long, the international community accepted high levels of violence and mayhem in the Congo, so long as it did not rebound against neighboring Rwanda, where prevention of instability after the genocide became an obvious priority.

After decades of misrule, war and predation by its neighbors — and a 1996 invasion of what was then Zaire by Rwanda, which brought down the three-decade-long dictatorship of Mobutu Sese Seko — some observers had given up on Congo and its population, by 2012, of 65 million. They even argued that the country, once a possession of King Leopold II of Belgium, no longer meaningfully exists as a state and that the international community should stop pretending that it does.

The recent military developments show the emptiness of this throw-up-your-hands approach. They also show that keeping a Band-Aid on the festering wounds of the Congo costs more, in lives, not just money, than taking resolute action....