Nigerian President Goodluck Jonathan’s decision last week to impose a state of emergency in the three north-eastern states of Borno, Yobe, and Adamawa, followed by air attacks, shelling and the deployment of troops, marks a dramatic new turning point for a country that last found itself at war more than four decades ago. The emergency is a response to the spread of the extreme Islamist group Boko Haram, which has led a violent insurgency since 2009; some 3,000 people are estimated to have died in the last three years, either as victims of Boko Haram or of army shootings. The government’s attempts to pursue dialogue via an amnesty committee have floundered on the intransigence of the group’s leadership but the military path Mr. Jonathan has now chosen is fraught with risk. There are already reports of the army using excessive force and arbitrary detention. The Ministry of Defence says the aim of its military operations is to reassert Nigeria’s territorial integrity. Boko Haram has a strong presence in the Borno state capital Maiduguri, where the fighting has caused enough fear and insecurity to make many residents flee their homes indefinitely.

Boko Haram, Hausa for “western education is sinful,” is the short name for the Jama’a Ahl al-sunnah li-da’wa wa al-jihad, or Congregation of the People of Tradition for Proselytism and Jihad. The group likely has al Qaeda links, and now uses sophisticated weapons, such as armoured vehicles with mounted machine guns. Boko Haram has kidnapped foreigners inside Cameroon, which abuts Borno, and earlier this year it forcibly recruited Borno youth. The group has also intimidated Muslims with bombings in Maiduguri and coordinated attacks in Kano, home to Nigeria’s largest urban Muslim population. Even the federal capital Abuja has been targeted; a 2012 attack on U.N. offices there killed 23 people. Boko Haram’s violent drive for a separate Islamist state taps into broad resentment that the country’s oil revenues have not filtered through to the north-east, Nigeria’s poorest region, but its goals are ideological. The fact that Boko Haram already has Chadians and Nigeriens in its ranks is proof of its ability to eventually contribute to the destabilisation of the wider region from eastern Mali to Chad. With the door to a political settlement all but firmly shut, Abuja can prevail provided its armed forces do not squander the advantage they have on the battlefield by allowing civilians to get caught up in the violence. President Jonathan surprised his domestic critics by acting boldly and decisively against the insurgents; he must now ensure that the manner in which force is used does not end up creating support for Boko Haram.