Complex sentence: Al-Walid was one of the most prominent Arabs fighting in Chechnya, and took over as Amir (commander) of an autonomous unit composed mostly of non-Chechen mujahideen following the death of its previous commander Ibn al-Khattab on 20 March 2002.
Split into simpler sentences: Al-Walid was one of the most prominent Arabs fighting in Chechnya. In 2002 he took over as Amir (commander) of an autonomous unit, composed mostly of non-Chechen mujahideen, following the death of its previous commander Ibn al-Khattab on 20 March 2002.