What made standard oil a horizontal integration monopoly?

Standard Oil became a horizontal integration monopoly because it owned ninety percent of US oil refineries.

In 1870, John D. Rockefeller and Henry Flagler established the well known American oil producing, transporting and refining company which eventually became a monopoly in Ohio. It became a monopoly because it bought almost all of the competitors so that it managed to control almost all oil production, processing, marketing, and transportation in the United States.

the church governed the society after the empire fell.   constantine took charge of rome and ended the confusion which had over religion and made christianity as the only religion and that started ruling the roman empire. he also divided the empire into two and fortified the eastern part.   he ruled the eastern part.