ow did the Muslims manage to conquer so much during the initial military expansion of Islam?

ow did the Muslims manage to conquer so much during the initial military expansion of Islam?

The Arabian peninsula is not exactly the most fertile place on the planet, and I have not heard about the Arabs having a codified, professional army or similar construction. So how did they manage to conquer so much territory from the Persians and Romans? How did they gather enough troops, take cities so fast, handle logistics, etc.?
slam was a force that was able to unite the various Arab tribes. It's possible that the Muslim warriors believed themselves to be fighting for God, and that Paradise could be their reward.

The weakness of both Persia and Byzantium was a factor, as they had been exhausting each other in war for the past several centuries.

The Arabs had excellent leadership-- specifically the caliph Umar, and the brilliant general Khalid ibn al-Walid.

The citizens of both Persia and Byzantium had grown discontent with their overlords. The Miaphysites (a Christian sect) of Syria disliked the fact that they were ruled by an Orthodox Christian Emperor from far-off Constantinople, and many of the conquered peoples thought of the Arabs as liberators. The Arabs also didn't impose their religion on the conquered peoples-- for example, it took two centuries for Islam to be become the dominant religion of Egypt.