Final answer:
The significant result of urban changes in large U.S. cities during and after World War II was increased social competition, with diverse populations striving for jobs and housing.
Step-by-step explanation:
During World War II and afterwards, large U.S. cities underwent significant changes due to experiments in technology and industrial productivity, which led to increased competition for jobs and housing. As more people flocked to urban centers for work opportunities presented by industrialization, cities expanded. Subsequently, a significant result of this pattern of urban changes was increased social competition. This development encompassed competition not only in the economic sense but also in terms of social dynamics as diverse populations sought to establish their place in the urban fabric.