What are the reasons for the successful conquests of the Arabs?

The Arabs really had a number of successful conquests, this was facilitated by several factors at once. The first reason was that all the rivals were rather weak, here the only exception could be the Sassanian state, which waged a difficult war for its statehood for twenty years. Also, the Arabs carried out a flexible socio-economic policy in the conquered lands, thanks to which many local residents went over to their side. For example, those who converted to Islam and sided with the winning side were exempted from many taxes.