Final answer:
The Federal-Aid Highway Act of 1956 and the growth of suburbs had a negative impact on the nation's cities by promoting suburbanization and displacing urban communities.
Explanation:
The Federal-Aid Highway Act of 1956 and the growth of suburbs both had a negative impact on the nation's cities. The Act, along with the development of highways, led to the suburbanization of the population, as people and companies moved away from city centers to suburban areas connected by these new road networks. This shift contributed to the decline and neglect of urban areas, affecting city structures and communities negatively.
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