The Great American streetcar scandal is a conspiracy theory in which streetcar systems throughout the United States were dismantled and replaced with buses in the mid-20th century as a result of alleged illegal actions by a number of prominent companies, acting through National City Lines , Pacific City Lines (on the West Coast, starting in 1938), and American City Lines .National, which had been in operation since 1920, was organized into a holding company, and General Motors, Firestone Tire, Standard Oil of California, Phillips Petroleum, Mack, and the Federal Engineering Corporation made investments in the City Lines companies in return for exclusive supply contracts. Between 1936 and 1950, National City Lines bought out more than 100 electric surface-traction systems in 45 cities,including Detroit, Cleveland, New York City, Oakland, Philadelphia, Phoenix, St. Louis, Salt Lake City, Tulsa, Baltimore, Minneapolis, and Los Angeles, and replaced them with GM buses. American City Lines merged with National in 1946.