During the American colonial period, what would become the Midwest was the backcountry, or the area behind the coastal population centers.
It was rural and rough, the sort of place that fueled populist resistance to the federal taxation of whiskey.
At the time of the Revolution, it was The West, often undifferentiated between north and south and largely associated with Kentucky.
In the early years of the republic, however, the regional differentiation deepened and grew until the latter half.