Secession (derived from the Latin term secessio) is the withdrawal of a group from a larger entity, especially a political entity, but also from any organization, union or military alliance. Threats of secession can be a strategy for achieving more limited goals.
The most famous secession movement was the case of the Southern states of the United States. Secession from the United States was accepted in eleven states (and failed in two others). The seceding states joined together to form the Confederate States of America (CSA).