That's the question a commenter poses, albeit with skepticism. First, the background here. New England was a peculiar society for various demographic reasons. In the early 17th century there was a mass migration of Puritan Protestants from England to the colonies which later became New England because of their religious dissent from the manner in which the Stuart kings were changing the nature of the British Protestant church.* Famously, these colonies were themselves not aiming to allow for the flourishing of religious pluralism, with the exception of Rhode Island. New England maintained established state churches longer than other regions of the nation, down into the early decades of the 19th century.
Between 1630 and 1640 about ~20,000 English arrived on the northeastern fringe of British settlement in North America. With the rise of co-religionists to power in the mid-17th century a minority of these emigres engaged in reverse-migration. After the mid-17th century migration by and large ceased. Unlike the Southern colonies these settlements did not have the same opportunities for frontiersmen across a broad and ecological diverse hinterland, and its cultural mores were decidedly more constrained than the cosmopolitan Middle Atlantic. The growth in population in New England from the low tends of thousands to close to 1 million in the late 18th century was one of endogenous natural increase from the founding stock.
This high fertility regime persisted down into the middle of the 19th century, as the core New England region hit its Malthusian limit, and flooded over into upstate New York, to the irritation of the older Dutch population in that region. Eventually even New York was not enough, and New England swept out across much of the Old Northwest. The last became the "Yankee Empire," founded by Yankees, but later demographically supplemented and superseded in its western reaches by immigrants from northwest Europe who shared many of the same biases toward order and moral probity which were the hallmarks of Yankees in the early Republic.
