I think that for more specific forces, more specificity in the question is required. I would say that one of the most relevant aspects of American History is the idea that the drive for political rights and economic rights have helped to shape the nation and lives of the people within it. The notion of political rights being the right to live and be free is something that has galvanized Americans into action. Westward Expansion was founded in part with the idea of religious freedom, such as the Mormons who sought to worship God in their own way. The notion of seeking a better life has been a part of Americans' desire to shape their own lives and nation accordingly. Economic rights has been a staple of American identity. The right to make and keep money has been something of tantamount importance to the development of America in that people have always sought economic security and prosperity within a nation that never possessed institutional inequality or something that precluded, at least openly, individuals from pursuing their dreams of material wealth. Notable exceptions to this would be women and people of color, specific African- Americans. Yet, over time, these groups, as well as other previously marginalized voices, were included in the American discourse rooted in the expansion and development of economic and political rights.
As asked, your question covers a great deal of potential ground (dissertation length a a minimum!) The first thing you will need to do is to narrow your focus a bit. If we start by considering the early American settlers, you are looking at two different groups of colonists. The Massachusetts colonies were established by a group of religious separatists (Puritans). The social force that most shaped their contribution to America cam in the realm of religion (and ultimately fostered a religious divide as they became prosperous in the new world and moved away from their church to form splinter churches). Another important contribution that cam from this group is the fact that they were writers, mostly of diaries and journals, but they wrote! William Bradford's "Of Plymouth Plantation" is an extended journal that forms the basis for all early American history textbooks that we still read today.The other early colonists, the Virginia colonists, came here looking for land and economic opportunities that did not exist for them in the "old world" so their motivations were entirely different.
Regardless of where they came from, however, the colonists were driven to control their own lives because they were escaping from a government (the monarchy) that they felt was too repressive. The Puritans sought religious freedom, the Virginians sought economic possibilities that did not exist under te crown. Both groups were driven by a search for identity that was not controlled for them but by them.
The intereseting thing here, however, is that in spite of the noble reasons for coming to the new world (freedom) these new Americans turned right around and created a new group of repressed individuals - first by repressing and isolating the Native Americans and then through the slave trade.
I think the best way to approach this is to first look at the forces themselves. The major social force would be religion, the major economic force would be a desire to achieve the "American Dream" and a political force would be to escape monarchy and the formation of a representative democracy.
This sounds to me like a question about the time from about the 1820s to the 1840s. This was a time when America's economy was changing. It was becoming more industrialized and more market-based. This meant that people who used to be independent farmers or master craftsmen were starting to be employees. This made them feel a loss of control in their lives.
One of the most important ways in which they sought control (historians say) was through religion. This was a time of renewed religious fervor (a Second Great Awakening) and of new religions (the Shakers and the Mormons, for example). The new religious fervor would clearly shape the lives of individuals who felt it. The emphasis on religion might also have shaped the US. It may explain to some degree why the US is so much more religious than most other rich countries.
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