Here’s a report from Global Security.org, “Behind Islamic State’s Battlefield Gains, Battle-Hardened Chechens”, which explains the Chechen contribution to the Islamic State’s successful military engagements. The report states:
“The Chechens aren’t the largest group among the thousands of foreigners in Syria, but they may be playing an outsized role, as many, battle-hardened by years fighting Russian forces, help spearhead the Islamic State’s sweeping successes through Syria and Iraq, experts said.
This bodes poorly not only for U.S. efforts to roll back the Islamic State in the near term, but also could mean a new cycle of violence is looming for Russia’s long-troubled North Caucasus.”