A History of American Political Theories is a comprehensive attempt to understand the full sweep of American political thought since the founding. Working within the liberal-progressive tradition, Merriam reviewed American political history in its entirety, from the founding down to his own day. He was not out to reduce political thought to a single element such as economics alone; his aim was to encompass the whole of modern social science.

The political science of the liberal-progressive tradition has roots and assumptions that were born in this period and nurtured by scholars such as Merriam. The progressive tradition in general and Merriam in particular interpreted the rise of a new science of politics that would be required for the liberal-progressive world view he represented. His work stands at a momentous fork in the road; two great traditions of how American democracy should be understood, interpreted, and analyzed parted company and afterward each went their separate ways. These traditions are represented, respectively, by the founders and the liberal-progressives. There was much at stake in these academic debates, though the consequences were not entirely foreseen at the time.

An overview of the authors, works, and general source material covered in History of American Political Theories is impressive. Merriam viewed the study of American democracy as an eclectic activity embracing the broadest definition of the social sciences, with particular emphasis on psychology. Such a transformation required that the social sciences be grouped as a whole rather than fragmented into separate and distinct academic departments.