What Was the Primary Factor Leading to Rapid Urbanization in the United

What was the primary factor leading to rapid urbanization in the United States between 1790 and 1820?

A) the growth of coastal cities resulting from rapidly developing international trade
B) increasing poverty rates that pushed rural workers off farms
C) hostile Indian attacks that caused settlers in the trans-Appalachian West to seek refuge in cities along the Atlantic seaboard
D) warfare between Britain and France that caused large number of farmers and small-town residents to move to cities, where they felt safer