Turner favored the Census Bureau definition of the "frontier line" as a settlement density of two people per square mile.
In the earliest days of European settlement of the Atlantic coast, down to about 1680, the frontier was essentially any part of the interior of the continent beyond the fringe of existing settlements along the Atlantic coast.
English, French, Spanish and Dutch patterns of expansion and settlement were quite different.
Otherwise lands east of the Mississippi River and what is now Canada went to Britain.
Regardless of wars Americans were moving across the Appalachians into western Pennsylvania, what is now West Virginia, and areas of the Ohio Country, Kentucky and Tennessee.