Why was it so difficult to rebuild the south after the civil war

There's a variety of reasons.  After the war, the south was quite literally, war torn, meaning everything was demolished or burning to the ground. After a war, both sides don't suddenly start accepting each other, and the civil war is no exception, there was a bunch of resentment back then due to the calamities of war.

Explanation:

Screwed up time but necessary

the factors that the economies of the muslim empires prosper were:

1- land trade routes-located between three continents  

2- sea trade routes

trade contributed to the spread of muslim empires, and with that islamic culture led to a growing feeling of internationalism resulted in the transfer of technology, science, and other cultural forms.