That’s less of a problem — the main problem is lower infant mortality leading to large family sizes; in my own tree a few generations back, one of three brothers who settled near here married into another large family; he had a niece who married one of his wife’s nephews, and from his other brother a nephew who married one of his wife’s nieces. At that time, given the lower overall population and sectarian isolations, it pretty much had to happen that way.
I looked at my family ancestry in Maine from 1626 on and they had enormous families. It was also not uncommon to marry cousins who lived at a distance.