>>17809731
- byzantines and persians waged long war and exhausted each other, financially and in terms of manpower, and population still didn't fully recover from justinian plague 100 years ago, that struck mainly large cities due to dense population (compared to desert tribes)
- middle east was a wreck, byzantines hadn't fully (re)consolidated the area after the war. picrel is PERSIAN largest extend
- autistic byzantine religious policy alienated levant and egyptian population that practiced "heresies"
- heavy taxation in both empires put a high strain on all population, when arabs came, they demanded LOWER taxes, gaining favor of locals
- less autistic religious policy, if you payed the jizya, nobody cared if your are monophysitist, miaphysitist, etc.
- use of roman and persian infracture
- arabian camels were highly mobile to counter heavy cavalry
- knowing their opponents and their tactics since arabs were always used in the region as mercenaries or allied tribes
- religious fanatism (motivation) and high morale, similar to the first crusade later