Around the 1930s, General Motors decided, together with other major corporations related to the auto industry, to form front companies which would buy up urban train and trolley lines in the United States (and attempted some Canada). From there trolleys were gradually killed off and disappeared. But who is responsible really?
Some Links:
The Trial: United States vs. National City Lines
Testimony from Bradford Snell
Criticism of the theory that General Motors was responsible
Some propaganda photos from that period