WHEN FRANCE dispatched troops to the West African nation of Mali a year ago, senior officials said they anticipated an operation of a few weeks — a temporary diversion from a policy of disengaging from “francafrique,” the zone of former African colonies that France informally managed for decades through financial, arms and business deals as well as military interventions. After French forces drove an ­al-Qaeda-linked militia out of Timbuktu, French Defense Minister Jean-Yves Le Drian rashly declared that “the mission has been fulfilled.”

A year later, more than 1,000 French soldiers are still fighting Islamic militants in Mali. Another French intervention force has been dispatched to restore order in the Central African Republic. And Mr. Le Drian is telling a very different story about his country’s role in Africa. In a visit to Washington on Friday, he said France had “assumed the responsibility” of filling a “security vacuum” in the continent that “could otherwise become a crossroads of trafficking and terrorism.”

For the government of François Hollande, this is a costly and risky initiative, and it deserves strong support from the United States. While the Obama administration retreats from areas where al-Qaeda is operating, Paris is reinforcing and reorganizing its military presence across the Sahel region. By the end of this year it expects to have 3,000 troops permanently deployed in four West African countries. That doesn’t count the 1,600 troops in the Central African Republic who, in theory, are engaged in an emergency mission but — as in Mali — likely will find it difficult to depart.

France is undertaking this duty despite growing fiscal pressures for the simple reason that its security and that of Europe face a serious threat from this part of Africa. Mr. Le Drian brought with him maps showing what he called a “corridor of trafficking” across Africa, from Guinea-Bissau in the west to the Horn of Africa in the east. The smuggling of drugs, weapons and humans is financing extremist groups, which are already concentrated in northern Mali and southern Libya and could spread to failed states such as the Central African Republic.

Combating these problems is a complex task. In addition to counterterrorism operations, African governments must be rebuilt and local armies trained to the point at which they can maintain security. France, in essence, is attempting to do in Mali and the Central African Republic what the United States and NATO tried to do in Afghanistan, albeit on a much smaller scale. It has made considerable progress in Mali, which now has a democratically elected president and an army-in-training, but it is only beginning in the Central African Republic, where a new president took over Thursday.

To its credit, the Hollande government accepts that these are long-term challenges; unlike the Obama administration, it has not set artificial deadlines for removing its forces. Mr. Le Drian says 1,000 French counterterrorism troops will remain in Mali indefinitely. There, as in much of the rest of northern Africa and the Middle East, the “tide of war” against al-Qaeda and its allies is not, as President Obama would have it, “receding”; in Africa, it is still coming in.