Arabia was not conquered by either the Byzantines or the Persians due to multiple factors such as the region being considered a backwater with limited resources and the weakened state of the empires during the Arab-Muslim expansion. The Arab-Muslims' fighting capabilities were another key factor in their successful conquests.
The reason why Arabia had never been conquered by either the Byzantines or the Persians is multifaceted. One reason is that much of Arabia appeared as a backwater to the Byzantine and Persian Empires, occupied by migratory and aggressive Arab tribes and offering few resources worth conquering.
Additionally, the timing of the Arab-Muslim expansion coincided with the weakened state of the Byzantines and Persians due to their long-lasting war, making it a prime opportunity for the Arab-Muslim raiders to strike.
Lastly, the hardiness and capability of the Arab-Muslims as a fighting force played a significant role in their success in expanding their territory.
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