American Cities, 1865 Through the Early 20th Century

What was one of the ways American city changed from 1865 to early 20th century? Analyze its historical significance? What was the short and long term effects did the transformation of American cities have on the nation?

I know that it was remarkable period of change in America roughly from 1865 to the early 20th century. Cities expanded at an incredibly rapid pace and went through a fundamental transformation in composition and construction. I need some help getting started with research as this is new learning.

My text is e Book
Bowles, M. (2011). A history of the United States since 1865. San Diego, CA: Bridgepoint Education