The jihadist group killed thousands of Yazidis, enslaved 7,000 and displaced most of the 550,000-strong community from their ancestral home.
Recruiters target vulnerable individuals and relocate cells created in Africa.
Rustam Azhiev, better known by his nom-de-guerre Abdul Hakim al-Shishani, led Ajnad al-Kavkaz in Syria and now leads Chechen fighters in the Ukrainian Foreign Legion.