Boko Haram insurgency insurgency spread to neighboring Cameroon, Chad, and Niger thus becoming a major regional conflict. In 2015, a coalition offensive forced Boko Haram to retreat into the Sambisa Forest. The insurgency took place within the context of long-standing issues of religious violence between Nigeria's Muslim and Christian communities. Boko Haram has been called the world's deadliest terrorist group, in terms of the number of people it has killed. Nigeria was amalgamated both the Northern and Southern protectorate in 1914, only about a decade after the defeat of the Sokoto Caliphate and other Islamic states by the British which were to constitute
Boko Haram Gwoza, which was believed to be the location of Boko Haram headquarters. On election day 28 March 2015, Boko Haram extremists killed 41 people, including a legislator, to discourage hundreds from voting. In March 2015, Boko Haram lost control of the Northern Nigerian towns of Bama and Gwoza to the Nigerian army. The Nigerian authorities said that they had taken back 11 of the 14 districts previously controlled by Boko Haram. In April, four Boko Haram camps in the Sambisa Forest were overrun by the Nigerian military who freed nearly 300 females. Boko Haram forces were believed to have retreated