I think the answer is b. Overgrazing occurs when too many animals graze for too long and exceed that of the area. Increased retention of water. It results in barren exposed soil.
By 1500, the Aztec Empire stretched from the Pacific Ocean
to the Gulf of Mexico, controlling 28 million people. By then, Tenochtitlan and
other nearby islands has fused into one great capital city, with an estimated population
of 400,000. They constructed a system of dams and aqueducts to control
lake levels and bring in fresh water from the mainland to supplement the
springs on the islands since then all else follows like their source of food
through the system of hydraulic agriculture, draining swampland and creating
artificial islands to grow food for the city. Making their civilization a successful
one.
The Union's industrial and economic capacity soared during the war as the North continued its rapid industrialization to suppress the rebellion. In the South, a smaller industrial base, fewer rail lines, and an agricultural economy based upon slave labor made mobilization of resources more difficult.
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