According to the quote, what happened between 1880 and 1890? the increase in settlements in the west caused the frontier line to disappear. the frontier line became isolated from settlements in the west. the size of the frontier line increased as settlers moved to the west.

The increase in settlements in the west caused the frontier line to disappear.

Explanation:

The finishing of the railways toward the West after the Civil War opened up vast regions of the district to settlement and monetary improvement.

The East settlement changed the Great Plains. The gigantic groups of American buffalo that wandered the fields were mostly cleared out, and ranchers furrowed the natural grasses to plant wheat and other crops. The buffalo loss had a great impact to the American natives and the development of white settlement influenced in the West.