How did the various achievements and policies of muhammad’s successors the arab world to grow?

There are many ways the policies and achievements of Muhammad's successors helped the Arab world. One of the main achievement was to unite the Arab under one flag instead of various tribes and communities, as the successors of Muhammad used the term "Khalifa" which was considered a unanimous leader of all the Muslims thus any territory that came under Islamic rule or any people who accepted Islam were united behind "Khlifa" instead of various leaders and tribal heads.
As there was a central system established in that time of succession, more focus was placed on developmental structures. For example in the time of Umar, the second successor various facilities were built for the travelers and those out on the road.
Trade and commerce evolved due to peace and stability provided by the central government as opposed to earlier times when caravans were looted in other tribal territories. 

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