Answer:
Religion
Step-by-step explanation:
During the 600s CE, an Arab expansion took place all over the Middle East. During these years, Muslim conquests became common, and this led to the establishment of unified Arabic empires, or "caliphates." This was a consequence of the common religion of Arabic groups: Islam. Their common religion allowed Muslim forces to fight in a unified way. Moreover, this religion gave Arabic people a reason to expand and conquer nearby groups.