From the Document: "Since 2009, an Islamist insurgency based in northeastern Nigeria has killed tens of thousands of people and triggered a massive humanitarian crisis in the Lake Chad Basin region of Nigeria, Cameroon, Chad, and Niger. Founded in the early 2000s as a Salafist Sunni Muslim reform movement, Boko Haram, which roughly translates to 'Western culture is forbidden,' has evolved into one of the world's deadliest Islamist armed groups. Since 2016, an Islamic State (IS)-affiliated splinter faction, the Islamic State's West Africa Province (IS-WA, aka ISIS-WA or ISWAP) has surpassed Boko Haram in size and capacity, and now ranks among IS's most active affiliates."
CRS In Focus, IF10173
Congressional Research Service: https://crsreports.congress.gov/