What is the appropriate term from systems theory for the part that directs and controls other parts of the system?

answer; the best answer is (demand);

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.

they could find out our specific needs.