Denominationalism is the inclination of religious groups to experience schisms and separate into different groups over disagreements about even very minor doctrinal matters. Why does this happen - why can't religious groups simply agree to disagree and remain part of a single organization?
According to H. Richard Niebuhr, denominationalism is largely a product not of religious forces, but rather social forces: class, racial/ethnic groups, regional divisions, and even nationalism. According to Niebuhr, these differences ultimately lead to ostensible religious differences and, hence, factional splits.
One primary factor which leads to this is the problem of comfort. As a religion becomes established, it becomes "comfortable" and supports the social status quo. As a result, it appeals primarily the middle class and those who are benefiting most from that status quo. Ethical teachings support how things already work rather than challenging society to become better. Radical interpretations of religious experiences are absent.
In such a context, those who are poor, in the lower class, in repressed groups, or otherwise on the margins of society become dissatisfied with the dominant religious orientation. Those who benefit least from society will also benefit least from the religion which offers theological justification for that society. As a result, they break off from the mainstream and form their own religious groups - groups which address their needs and offer them hope in their suffering.
Typically in such a new religious movement, their social group is validated as the most worthy and the most holy. It is the poor or the meek who will inherit the earth and the wealthy who will suffer in the afterlife, if the group speaks to the poor, like early Christianity. Or perhaps it is the Africans who will receive the highest blessings of God and the Satanic Whites who will suffer God's wrath, as taught in the early days of the Nation of Islam.
At first, such new groups do not yet constitute religions in the sociological sense. Instead, they tend to be called cults or sects. It is only after they, too, become more established and maybe even a bit comfortable that they finally receive the label "religion" in academic circles. In the process, the character of the religious group changes along with the changing nature of the social group.
This continues to happen, over and over, as people who form one social group or another find that their religious organization does not speak to their social needs. This is, obviously enough, dependent upon a sociological explanation of religion - it assumes that religions exist for social reasons and for the purpose of serving social needs. Those who reject sociological explanations of religion may tend to reject this sociological explanation of religious division as well.
