The first Americans (assuming you mean colonists, not Native Americans) were committed to the ideas of personal freedom because many of them had come to America for the sake of freedom. A number of the colonial settlers had left Europe in order to find freedom to practice their religion as they wished, for instance.
For the colonists in the days leading up the the American Revolution, personal liberties and rights were a paramount concern. The leaders in colonial America had studied Enlightenment arguments concerning the rights of persons and personal liberties. A main philosopher who advocated personal freedom--and was read by the American founding fathers--was John Locke. According to Locke's view, a government's power to govern comes from the consent of the people themselves -- those who are to be governed. This was a change from the previous ideas of "divine right monarchy" -- that a king ruled because God appointed him to be the ruler. Locke repudiated the views of divine right monarchy in his First Treatise on Civil Government. In his Second Treatise on Civil Government, Locke argued for the rights of the people to create their own governments according to their own desires and for the sake of protecting their own life, liberty, and property.