The correct answer is Arabs.
The Abbasids sought to lessen the power of the Arabs by moving the capital to Baghdad.
The Abbasids was a great Muslim dynasty that ruled the Empire from 450 CE until 1258 when the Mongols invaded its territory. The powerful Abbasid caliphate moved the capital from Syria to Baghdad to lessen the power of the Arabs. Being in Baghdad, the capital was close to the Persians who were allies of the Abbasids.