The Ku Klux Klan, commonly called the KKK or simply the Klan, refers to three distinct secret movements at different points in time in the history of the United States. Each has advocated extremist reactionary positions such as white supremacy, white nationalism, anti-immigration and—especially in later iterations—Nordicism and anti-Catholicism. Historically, the KKK used terrorism—both physical assault and murder—against groups or individuals whom they opposed. All three movements have called for the "purification" of American society and all are considered right-wing extremist organizations. In each era, membership was secret and estimates of the total were highly exaggerated by both the friends and enemies.