Haiti’s spiraling mayhem, florid lawlessness and humanitarian meltdown were predictable following the assassination of President Jovenel Moïse in July. In a country already crippled by governmental dysfunction, the vacuum of political legitimacy and authority after that murder left a breeding ground for anarchy.

The mess was largely ignored by the Biden administration, which has been preoccupied with other crises, until the kidnapping Saturday of 17 missionaries — a Canadian and 16 Americans, including five children — near the Haitian capital of Port-au-Prince. Now the maelstrom in the hemisphere’s poorest nation is no longer ignorable.

Kidnapping is so prevalent that predatory gangs which routinely seize individuals and groups for ransom are now said to control half of Port-au-Prince. One of the more notorious of them, 400 Mawozo, is responsible for the missionaries’ kidnapping; earlier this year it grabbed five priests and two nuns and demanded $1 million for their release. They were eventually freed.

Haiti’s outmatched police are bystanders to the spreading pandemonium, and the government, which includes no elected officials, is window dressing. The fate of the missionaries is anyone’s guess, but no one should assume that their seizure is an aberration, or that Haiti’s dissolution will not generate further agonies for its own citizens and those of other nations. Those agonies will include desperate migrants at the United States’ border, such as the thousands who camped under a bridge in South Texas last month, seeking a foothold in this country.

There are no easy answers to fixing Haiti, nor even to what “fixing” it might mean. Some advocates insist that the key to rescuing Haiti lies in its civil society, the country’s vibrant network of nongovernmental social, educational, health and other organizations that provide what passes for a social safety net and a counterbalance to chaos. The truth is that those multifarious groups, for all their important work, are as splintered as the rest of Haitian society and just as powerless to arrest the country’s disintegration.

Those who called for international intervention following Mr. Moïse’s killing, including this page, have been criticized for overlooking the checkered history of such attempts in the past, including the U.S. Marine Corps’s 19-year occupation of Haiti a century ago, and the United Nations-authorized insertion of U.S. troops by the Clinton administration in the mid-1990s. In this century, a U.N. stabilization force was deployed in Haiti for 13 years, until 2017.

Those interventions were problematic. In the most recent instance, U.N. soldiers sent to Haiti from Nepal were the conduit for what became one of the world’s most severe cholera epidemics, and other U.N. troops fathered hundreds or more babies born to penniless local women and girls, amid credible allegations of rape and sexual exploitation.

Yet for all its unintended consequences, outside intervention could also establish a modicum of stability and order that would represent a major humanitarian improvement on the status quo, and with it, the prospect of lives saved and livelihoods enabled. In the cost-benefit analysis that would attend any fresh intervention, policymakers must be alert to the risks, but also to the enormous peril of continuing to do nothing.