secession (n.)
1530s, from Latin secessionem (nominative secessio) "a withdrawal, separation; political withdrawal, insurrection, schism," noun of action from past participle stem of secedere "secede," from se- "apart" (see secret) + cedere "to go" (see cede). Originally in a Roman historical context, "temporary migration of plebeians from the city to compel patricians to address their grievances;" modern use in reference to religious or political unions dates from 1650s.