Who are the jihadists using the Sahel as a hunting ground?

Tens of thousands of people have been killed in violence which began in Mali in 2012. [AFP]

For well over a decade, jihadist violence has plagued the Sahel, a semi-arid belt stretching along the Sahara desert's southern rim from the Atlantic to the Red Sea.

Tens of thousands of people have been killed in violence which began in Mali in 2012, spread to Burkina Faso and Niger, and now threatens coastal west African states.