The teaching of American history has long concentrated on the victors and not on the other elements of society. For example, only since the Civil Rights movement have historians concentrated on studying the lives of enslaved people. However, it's essential to study not just the dominant groups but groups on the margins of society.
Studying these groups gives a fuller picture of society than just the study of the dominant groups does, and the study of less dominant groups also provides a critique of society at different points. Dissenters teach us what might have been wrong with American society at different points and the ways in which the liberty and justice promised to all Americans was not a reality.
Studying groups with less power provides a fuller view of what was going on at the time, as these groups are larger in nature. In addition, marginal groups formed the main force of many movements in American history.
For example, the Second Great Awakening, which took place around 1800, was a movement that involved women, African Americans, and the poor. They were major components of the movement, and to understand this movement, one must look at the actions of those who were dispossessed. Studying just the major players, or those who received notice at the time, obscures the important roles of the dispossessed.