Founded by Mohammed Yusuf in 2002, the group was led by Abubakar Shekau from 2009 until his death in 2021, although it splintered into other groups after Yusuf's death and also in 2015. When the group was first formed, their main goal was to "purify" Islam in northern Nigeria, believing jihad should be delayed until the group was strong enough to overthrow the Nigerian government. The group formerly aligned itself with the Islamic State of Iraq and the Levant. The group has been known for its brutality, and since the insurgency started in 2009, Boko Haram has killed tens of thousands of people, in frequent attacks against the police, armed forces and civilians. It has displaced 2.3 million from their homes and was during part of the mid 2010s the world's deadliest terror group according to the Global Terrorism Index. Boko Haram has contributed to regional food crises and famines.