As noted, an ideology is a set of political beliefs about the nature of people and society. People who are committed to an ideology seek not only to persuade but to recruit others to their belief. In U.S. history, there are many examples of extremist ideologies and movements. The colonists who sought to free themselves from British rule and the Confederate states who sought to secede from the Northern states are just two examples.
Nowadays, instead of dressing in sheets or publicly espousing hate messages, many extremists will talk of individual liberties, states’ rights, and how to make the world a better place.