Why did the ku klux klan form?

The Ku Klux Klan (/ˈkuː ˈklʌks ˈklæn, ˈkjuː/),[a] commonly called the KKK or the Klan, is an American white supremacist hate group[8] that was founded in 1865 during the Reconstruction era. The Klan has existed in three distinct eras at different points in time during 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[9][10] and anti-Catholicism. Historically, the KKK used terrorism—both physical assault and murder—against groups or individuals whom they opposed.[11] All three movements have called for the "purification" of American society and all are considered right-wing extremist organizations.[12][13][14][15] In each era, membership was secret and estimates of the total were highly exaggerated by both friends and enemies.