Complex sentence: The Kel Gres are a Toureg confederation of clans (or "Drum-groups") who in the modern era have mostly lived in south central Niger, though who have a history of occupation of the Aïr Mountains prior to the 17th century.
Split into simpler sentences: The Kel Gres is a confederation of Toureg clans (or "Drum-groups"). In the modern era, they have mostly lived in south central Niger, though they are known to have inhabited Aïr Mountains prior to the 17th century.