Presenting an analysis of modern-day extremism, this book explores how any group or movement--political, ideological, racial, ethnonational, religious, or issue-driven--can adopt an extremist mindset if they believe their existence or interests are threatened. Looking beyond "fringe" resistance groups already labeled as terrorists or subversives, the author examines conventional organizations--political parties, religious groups, corporations, interest groups, nation-states, police and the military--that deploy extremist strategies to further their agendas. A dynamic of mutual causation between conventional and resistance groups is argued: extremist resistance surfaces in response to oppressive measures by conventional powers to maintain their supremacy through systemic injustices, including slavery, caste systems, patriarchy, colonialism, autocracy, exploitive capitalism, and discrimination against minorities.