Few events have dramatically altered the course of world-history as have the dynamic Muslim conquests of the seventh century. Aside from the seizure of a large expanse of onetime Roman lands and the cultural Arabization of millions of people, great wars have been continuously waged between Islam and the West- till the present. Yet ambiguity abounds as to how and why these conquests were first realized. This study seeks to ascertain the immediate factors behind the conquests in general by deconstructing the all-pivotal Battle of Yarmuk in particular. This paradigmatic encounter is ideal for extrapolating the root cause(s) of the conquests; for it was primarily at Yarmuk that the Arabs suffered notable physical and practical disadvantages-and still emerged triumphant. Thus this engagement allows one to see well beyond the usual aspects of military history- the physical and practical-and better appreciate more abstract yet decisive considerations.