The main motivation was GOLD. but if you need more options EXPANSION OF TERRITORY would work too. Have a good day, Hope this helps:)
I'm not 100% sure but it could be: Voluntary Exchange takes place between buyers and sellers:
(btw I copied and pasted from the question so I didn't take any content :D)
Minimal government involvement in the economy.
It can either bring people together into a new fused culture, or it can diffuse them. If various people exist of various cultures and a new empire rises then the leader has to accept all the people into his empire. This means that the cultures all exist and since they all have to behave according to what the emperor says, the cultures often mix and create somewhat of a mixed culture.If the empire separates people then it leads to diffusion because new aspects of cultures develop independently.
