If you want an illustration of the law of unintended consequences, look no further than Mali. The drama that’s been unfolding there over the past nine months, and that has taken a new turn in the past week, is a perfect illustration.

Here’s the background. Muammar el-Qaddafi's regime began to crumble under the combined onslaught of NATO airstrikes—which began with the then-president of France, Nicolas Sarkozy, launching his jets even though the other participating NATO states had planned to act in unison—and the increasingly effective ground operations of the Libyan opposition. Ethnic Tuaregs, whom the Libyan dictator had long used as mercenaries, feared that they would face reprisals and fled to neighboring Mali.

They took lots of weapons with them, supplementing the long-running efforts of Malian Tuaregs to create an independent homeland in the north. The Tuaregs, distributed across various North African countries, had sought their own state in vain as France was withdrawing its empire in Africa’s north and west following World War II. They now sensed a long-awaited golden moment.

Before long, the Tuaregs carved out an area equal in size to France in Mali’s north. Malian army units, trained by the United States, either fled or Tuareg soldiers and commanders defected to the insurgents, taking their weapons with them. The main army in southern Mali, also U.S. trained, overthrew the elected government, creating even more chaos.

Since then, the demarcation line between northern and southern Mali has remained stable. In the north, the Islamist elements of the insurgency vanquished their nationalist brethren. They then built a draconian sharia-based state, which amputates the limbs of thieves, imposes all manner of restrictions on women, and has created an atmosphere laden with fear.

But the Islamists seemed content to hold the ground they had—until last week. Suddenly, they crossed the demarcation line, capturing the town of Konna. The Malian government, fearing that the next target would be the airbase at Sevare, and then town of Mopti, as a prelude to a drive toward Bamako, Mali’s capital, panicked. With their army manifestly ill-prepared to meet the challenge—it has steered clear of the north—Mali’s leaders appealed to France, long the dominant European power in the region, a legacy of its former empire.

Enter France, which soon faced some unpleasant surprises. When it launched airstrikes to drive the Tuareg Islamist guerrillas from Konna, and the towns they had taken in the north, the latter predictably ensconced themselves in the homes of civilians, forcing France to face the fact that the air strategy would kill innocents and create a backlash—precisely what the insurgents want.

Then, as a further surprise, the Tuareg warriors took Diabaly, west of Konna and a mere 200 miles from Bamako. The insurgents have been pummeled by French air attacks but they have dug in and possess plenty of weapons, stored in underground redoubts. Plus, they’re not going to go toe-to-toe with French troops; that would be dumb, which is why they have since abandoned Konna and Diabaly. Instead, they’ll launch other diversionary attacks as they did in Diabally and retreat to Mali’s rugged outlying areas, hoping to draw the French into the vastness. Even if France beefs up its contingent to some 2,500 (which seems to be the plan), its troops will have to cover a huge area, making themselves vulnerable to ambushes.

The French want to avoid a protracted war. To that end, they plan to hand off to Malian forces, which are already helping them, and to others from surrounding states: Niger, Nigeria, Mauritania and Burkina Faso.

But that plan faces problems. What if the African troops can’t hold the line, let alone retake the north, and the emboldened Tuareg Islamists push south again?  

In addition, the insurgents might resort to what war wonks call asymmetric attacks and horizontal escalation—in plain English, unconventional operations aimed at Western interests far from the battlefield. The attack on the Algerian gas field at In Amenas, located near Algeria’s border with Libya, by an Islamist group allied with the main Malian Tuareg Islamist group, Ansar Al-Dine, is a textbook example.

This operation captured some 40 Western hostages, including from France and the United States, as well as from Britain and Norway, whose oil companies are helping Algeria’s state oil company, Sonatrach, run the field. A number of hostages were killed when the Algerians launched a rescue.

Then there’s the possibility of attacks in France itself—harder to pull off but scarcely impossible—or on French citizens or installations in north and west Africa, which would be easier to do.

President Francois Hollande has inherited the fallout from his predecessor’s Libyan venture, and France could find itself in just the pickle it wants to avoid. And the United States and Britain, who have said they’ll limit themselves to providing France and the African troops indirect support (logistical and intelligence), may have to decide whether to let France twist in the wind. Doing so would hardly be good for NATO solidarity. Getting in deeper could create a range of risks.

Qaddafi’s fall initiated an unanticipated chain reaction and Mali’s U.S.-trained army was overwhelmed by it. This campaign is far from over. And it validates another lesson (the first being the risk of unintended consequences): It’s easy to start military operations, but as the great theorist of war Karl von Clausewitz warned, what’s predictable about war is its unpredictability. Clausewitz called this problem “friction.” Friction can shred even the best-laid plans. And it could do so in Mali.