Question

How did John D. Rockefeller horizontally integrate his monopoly in 1880?

Answer 1

He created a trust that controlled ninety percent of the nation's oil refineries.

Answer 2

Rockefeller used the size of his company Standard Oil to negotiate preferential rates with railroad companies to transfer his oil in the refinement process. By gaining the upper hand in transportation costs, he was able to horizontally integrate his competitors into his firm working to establish a monopoly in the American oil industry. I hope this helped. :)