In Frederick Jackson Turner's "Social Forces in American History" (1910), he discusses the role of the populist agrarian movements in the politics of the United States:
Read the platforms of the Greenback-Labor, the Granger, and the Populists parties, and you will find in those platforms, discredited and reprobated by the major parties at the time, the basic proposals of the Democratic Party after its revolution under the leadership of Mr. Bryan, and of the Republican Party after its revolution by Mr. Roosevelt.
Solon J. Buck - in The Agrarian Crusade - traces the involvement of farmers and Westerners in the development of political movements and parties which agitated for further government interference in the American economy, especially agriculture - presumably on behalf of the farmer and in opposition to merchants and middlemen. Some of these groups even being branded as advocating socialism and/or communism (some such as the Greenback Party did occasionally have socialists at their conventions). These parties and movements would eventually collapse, but not before catching the attention of the major parties and fusing with them (mostly with the Democratic Party). We often think of the Democratic Party at this period as being rather conservative, but on economic matters it was becoming quite progressive, and this pattern would continue into the 20th Century with the elections of Woodrow Wilson and later FDR. Grover Cleveland was perhaps the last Democratic president who stood for classical economic principles (Coolidge the last Republican to do so).
The men of the West - the frontiersmen - and the farmer had evolved into a social force to fight monopolies, special interests and industrialists, while the masters of industry saw themselves as taking on the spirit of pioneer individualism.One can see this trait even in today's contemporary ideologies, wherein big business is either regaled as the spirit of individualism or decried as anti-social.
Some other books which discuss this topic: