Zinn's historical focus is on marginalized groups in American history. Zinn sees the Progressive movement as a way to combat socialism by enacting social reforms without going toward socialism. Zinn overstates the socialism movement in the United States. While its main presidential candidate, Eugene Debs, gained votes, he was never a viable presidential candidate. Unlike other movements, such as the Populist movement, the Socialist party's principles were never fully adopted by either major political party. Contrast this with Progressivism, which was adopted by both major political parties at the turn of the twentieth century under the heading of "reforms."
Socialism was an important movement, and it reflected a worldwide trend of workers voicing their complaints against the ultra-rich, who were only getting richer. Many people balked at true socialism, however, as they saw their economic status as being upwardly mobile—one day, they figured, they or their descendants may become rich. While socialism was a part of the American political conversation, it was not as powerful as Progressivism or Populism in changing political parties and ultimately changing the relationship the average person had with the federal government.