Fighting terror, together? The questions facing France and West Africa.

When French President Emmanuel Macron summoned the presidents of Mali, Niger, Chad, Burkina Faso, and Mauritania to the French city of Pau for a summit on counterterrorism last week, the backdrop was somber.

Two months earlier, during a late night anti-terror operation in Mali, two French military helicopters had collided in the moonless sky, killing all 13 soldiers on board. It was the French military’s highest single-day death toll since 1983. Meanwhile, in the capitals of Mali, Niger, and Burkina Faso, protestors marched in the streets with a message for Mr. Macron and his troops. “France,” their signs read, “Get out.”

The soldiers’ deaths, combined