Question

What factor is primarily responsible for the sharp contrasts between Old World and New World civilizations?

Answer 1

Probably the incredible independence (or maybe last-ditch efforts) of the people who completely uprooted themselves to get on ships and move themselves and their families to a completely unknown place.

Religious freedom also was a factor for many.

http://www.digitalhistory.uh.edu/era.cfm?eraid=2
Read, read, read ... and then let us know what you discover.

Answer 2

Traditions