Defectors from a homegrown jihadi insurgency in the Caucasus are now on Team Caliphate. Here's what that means.

At the same time as bombs rain down on the Islamic State, and it grapples with tactical setbacks in Syria and solidifying their hold in Iraq, ISIS continues to expand its brand, this time in the Caucasus. In June, one of the most important and respected rebels in the North Caucasus pledged loyalty to IS.

The defection of Amir Khamzat, commander of the Chechen Vilaiyat, [territorial-administrative units that roughly correspond with the regional republics], represents a large gain to the standing of IS and its expansion into Russia. A statement posted [to Twitter] on June 21 read: "We testify that all Mujahideen of the Caucasus—in the Velayats of Nokhchiycho [Chechnya], Dagestan, Galgaicho [Ingushetia] and KBK [Kabarda, Balkaria and Karachay]—are united in their decision and we do not have differences among ourselves." This statement led ISIS on June 23 to embrace the pledges of loyalty and declared the creation of a new Vilaiyat under the control of Dagestani Amir Rustam Asilderov, also known as Abu Muhammad al-Kadarskii.

Estimates of the size of the insurgency are hard to come by, as Russian official statistics are notoriously unreliable, and the autonomous nature of the insurgency means local cells size can fluctuate with the seasons and a revolving door of committed recruits.