(7.6D-2) An economic impact of the agricultural industry resulting from the
close of the frontier -
caused many farmers to declare bankruptcy.
ended cotton farming as a cash crop.
made cotton farming an ideal cash crop.
forced the railroad industry to shut down

made cotton farming an ideal cash crop.

Explanation:

After the close of the frontier, Railroads company took enough ownership of western territory to finish the rails that connected a lot of states.

This make it possible for southern states tho produce large amount of Cotton to distribute their product nationwide. As a result, cotton become an ideal cash crops (plants that generate large profit) . It contributed to a very large portion of southern economy.

after the french-indian war.

the national congress's powers over the states were specific and definite: it had the sole power to negotiate treaties, declare war, and make peace. all powers not granted to congress were reserved for state governments. congress had no power to levy taxes, for example.