The Mongol invasion of Persia (from 1220), drastically changed the socio-political environment of the region. During this period, Shiite theology became established, and Sufism became erfan (gnosis) and penetrated deep into Persian lyrical poetry. The musical style of Araq (western Iran) gradually adopted the structure and emotional language of ghazal (a form of Persian poetry) and poetry became the main source of avaz (vocal section). During the 16th to 17th centuries, Persian music began to follow its own course and diverged from that of its Arabic, Turkish, and Tajik neighbors.