Secession is the act of withdrawing formally from a federation or other political union. It usually involves the creation of a new, independent government.
Here are some examples:
* The secession of the Southern states from the United States in 1860-1861 led to the American Civil War.
* The secession of Catalonia from Spain is a current political issue.
* The secession of Scotland from the United Kingdom has been a topic of debate for many years.
While "secession" is the most precise term, other related words you might consider include:
* Independence: The state of being free from the control of another country.
* Autonomy: The right to self-government.
* Separation: The act of becoming distinct or separate.