In A People's History of the United States, how does Howard Zinn describe the development of socialism during the Progressive Era?

In Chapter 13 of
, "The Socialist Challenge," Zinn describes socialism as arising
from class anger that developed in response to the harshness of ordinary life. Famous writers
such as Mark Twain and Jack London were incensed by American military actions abroad during the
Spanish-American War and by the reality of life for the working class. As a result, they were
drawn to socialism.

In addition, Zinn writes that hundreds of thousands of
ordinary American workers were drawn to socialism in reaction to the police crackdown on
strikes, as the police and the law took the side of business owners. As a result, socialism
began to spread from circles of Jewish and German immigrants to states such as Oklahoma, where
socialism took root among tenant farmers, coal miners, railroad workers, and other members of
the working class. It also appealed to feminists.

Socialism was, in fact, so
popular that progressivism arose as a response to socialism. Zinn writes...