The 7th-8th-century Muslim forces of the Middle East espoused both mobility and tactical prowess, with their manpower mainly drawn from the already urbanized tribes of the Syrian heartland. However, as the Umayyad Caliphate expanded, the forces of the frontier regions were composed mostly of the mawalis (clients) – basically voluntarily-converted adherents of Islam from the non-Arab background, like the Persians in the Khorasan region and the Berbers in North Africa (Maghreb). And it was the latter who played an instrumental role in the conquest of the Iberian peninsula (in early 8th century AD) – most of which was under the control of the Christian Visigothic Kingdom.
In the century before the conquest of Iberia (Spain and Portugal), the Berbers of North Africa were a disparate people dominated by authoritative tribes with varying religious affiliations, ranging from indigenous pagan beliefs to even Judaism. By 7th century AD, the Eastern Roman grasp on this region had already dissipated, and the power vacuum was filled by the Arabs approaching from the direction of Egypt (who were rather aided by the small yet Romanized urban population). More here on Realm of History