Khālid's incomparable talents. According to Athamina, Medina's lack of a regular standing army, the need to redeploy fighters to other fronts and the Byzantine threat to Muslim gains in Syria required the establishment of a defense structure based on the older-established Arab tribes in Syria which had traditionally served as confederates of Byzantium. After Medina's entreaties to the Ghassanids were rebuffed, relations were established with the Banu Kalb, Judham and Lakhm. The local tribes likely considered the large numbers of outside Arab tribesmen in Khalid's army as a threat to their political and economic power. Khalid's initial force of 500-800 men had swelled to as high as 10,000 as a result of tribesmen joining his army's ranks from the Iraqi front or Arabia and as high as 30,000-40,000 factoring in their families. Athamina opines Umar dismissed Khalid and recalled his troops from Syria as an overture to the Kalb and their allies.