How did the growth of American cities affect social, cultural, and political life?

Generally cities cause people to become more liberal, have a social hierarchy, and promote the general abundance of transportation.

Explanation:

Socially, you can have tenements form, races can self and forcefully segregate, and people tend to become more liberal with exposure to other races.

Cultural is kind of related. People tend to clump into ideological groups (if you can give me the context of the question I can better answer).

Political life, like I said they tend to become more liberal. If your question is centered around the 1920's you could discuss child labor laws.