That may be dependent on where you went to school:
War of Separation/Secession
“War of Separation” was occasionally used by people in the Confederacy during the war. In most Romance languages, the words used to refer to the war translate literally to “War of Secession” […], a name that is also used in Central and Eastern Europe: Sezessionskrieg is commonly used in German language, and Wojna secesyjna is used in Polish. (Walt Whitman calls it the “War of Secession” or the “Secession War” in his prose).
That may be dependent on where you went to school:
Wikipedia: Names of the American Civil War