The initial success of the Christian crusaders came through an exceptional ability to mass troops to repel attacks by a disorganized and a defunct Moslem alliance to defeat a common enemy. Although short on manpower (see above answer), in the earlier period of Christian states in the East, there was a realization of the importance to ward off Islamic attacks in one state to ensure the security of another--and the rulers of these states were sure to support each other (in the beginning--but eventually the continuous raids caused each Frankish prince to defend his own defenses (Beeler 123)). In early 1111 the Moslems began the launching of annual, yet seasonal, attacks, as the Suljuk Sultan of Baghdad seemed determined to expel the Christian invaders from the east.
Fortunately for the Christians, the emergence of a strong Islamic ruler continued to divide the Muslim states, and as Bursuq ben Bursuq, ruler of Hamadan, was appointed as the commander of an expedition to assault the Christian frontier in 1115, the rulers of some of the smaller states opted to ally with the Franks as opposed to subject themselves to the rule of Baghdad.
As Bursuq mustered his forces and began his approach towards Antioch, Prince Roger and his Syrian Muslim allies of Damascus, Madin, and Aleppo prepared their defenses (Prince Roger in person) along the Moslem frontier, additionally establishing a base of forward operations at Afamiya (Beeler 131-2).
From this base, Roger was able to establish reconnaissance patrols as far as Mesopotamia, ensure the kingdoms of Hims and Shaizar were discouraged from supporting Bursuq, and apply an immediate repelling attack on Aleppo, Antioch, or Damascus. Furthermore, the Afamiya base contained enough supplies that Prince Roger and his allies were able to avoid battle on the open field, and thwart Moslem attempts at...