Baltimore’s streetcar system was dismantled by National City Lines (NCL) in the period of 1948-1965. NCL, a holding company formed by General Motors, Firestone Tire and Rubber, Standard Oil of California, and Phillips Petroleum, acquired or controlled 46 transit systems for, as one author put it, “the express purpose of acquiring and dismantling urban streetcar operations. In so doing, they allegedly created lucrative and long-term markets for their own products. ” 
In the early to mid-1940’s two-thirds of all trips generated by Baltimore residents were via public transit, most on the trolley system. 

See also, the Maryland Center for History and Culture article, “Lost City: Baltimore’s trolleys, trackless trolleys, and buses.” 

Photo and video credit to Baltimore Heritage