Final answer:
The most diverse population of immigrants in the Middle Colonies was mainly due to religious tolerance, attracting a variety of settlers and developing a pragmatic, accommodative society.
Step-by-step explanation:
The cause of the most diverse population of immigrants in the Middle Colonies was religious tolerance. As history shows us, the region became a melting pot of various cultures and religions partly due to the patterns of settlement under Dutch rule, which were characterized by a liberal approach to religious worship. Over time, these settlements became known for religious toleration, attracting settlers from a multitude of backgrounds, including Belgium, France, Scandinavia, Germany, and dissident Puritans from New England. Moreover, the influence of Quaker beliefs in Pennsylvania, established under William Penn, also promoted a policy of religious freedom and peaceful coexistence with Native Americans. It was this tolerance and the pragmatic, accommodative spirit of the colonists that shaped the unique and mixed society of the Middle Colonies.