"Secede" means to formally withdraw or separate from a group, organization, or country, usually because of differences or disagreements. Full definition
Worse still, when political opponents saw the calisthenics training sessions of the pupils in 2012, they immediately alleged that Aregbesola was training the youths as armed militias, who would be used to assist his state in seceding from Nigeria! (nigeriapoliticsonline.com)
Among the highlights was the panel on segregation with Hechinger's Emmanuel Felton, who wrote about school districts seceding in Jefferson County in Birmingham, AL. «We wanted to zoom in on where segregation was getting worse the most rapidly,» said Felton. (kappanonline.org)
The question of secession was resolved as a practical matter by the American Civil War, and as a matter of law by the Supreme Court decision Texas v. White, in which it was ruled that states can not unilaterally secede from the Union and did not do so during the Civil War. (politics.stackexchange.com)