The Cleveland Massacre was significant in the formation of Standard Oil because it became a monopoly in the Cleveland oil market after the Massacre.
Explanation:
In 1870 John D. Rockefeller created what would be his flagship company: the Standard Oil Company, and began combining efficient management with the use of tools not entirely legitimate (and sometimes openly illegal) to defeat his competition. The best known would be his dealings with railway companies to make him large-scale rebates and charge more to his competition in exchange for exclusivity in transport. At that time the Standard Oil was already giant, and negotiate with it was a privilege, so many accepted unleashing a scandal that would disrupt the reputation of the company (it must be accepted, however, that this business provided many people the ability to use kerosene, as the product was much more expensive before the Rockefeller-driven price war, and the whale oil used before was even more expensive).
In 1872 the so-called "Cleveland Massacre" occurred. In a period of just 4 months, taking advantage of a drop in prices, Rockefeller was able to buy 22 of the 26 refining companies that competed with him in Ohio, leading even his fiercest competitors to prefer an alliance to a war. The company's growth was overwhelming and by the end of the decade Standard Oil refined 90% of US crude. Whenever possible, the tycoon offered a new petroleum-based product, increasing its sales base and making its production more efficient.
