Complex sentence: By December 2012, it had grown to eight brigades, which were formed in Afrin, al-Qamishli, Kobanî and Ras al-Ayn.
Split into simpler sentences: By December 2012, it had grown to eight brigades. Some of these brigades operate in Afrin, al-Qamishli, Kobanî and Ras al-Ayn.