"by the beginning of the eighteenth century land scarcity pushed both native-born and newly arrived families to look westward." descendants of old yankee families would establish themselves while european immigrants found more luck

I believe the answer is:  in frontier New England; south of New York

The division of these territories is more influenced by cultural factors rather than geographical factors.

The immigrants found more luck in south of new yorks because many descendants from british colony settled in this area after the revolutionary war, because there is a greater atmosphere of acceptance towards non locals in this area. The yankees on the other hand settled in frontier new england which have stronger christian culture.