By 1900, andrew carnegie controlled about 25% of the nation’s output.

By 1900, Andrew Carnegie controlled about 25% of the nation’s steel output.

Explanation:

Andrew Carnegie was an American industrialist, businessman and philanthropist from Scotland. As a child, he emigrated from Scotland with his parents. He worked from a very young age on the Pennsylvania Railroad Company. At age 20 he became manager of the same railroad company and the apprentice of Thomas A. Scott, owner of the company.

He created the Carnegie Steel Company in Pittsburgh, which later merged with the Federal Steel Company of Elbert H. Gary and with several smaller companies to create U.S. Steel. The fortune he earned from his businesses was spent on philanthropy and education, founding the Carnegie Corporation of New York, the Carnegie Endowment for International Peace, and Carnegie Mellon University in Pittsburgh.

these civilizations were located around fertile rivers, where they could produce an abundance of crops