secede

verb2

1. •
   To split from or to withdraw from membership of a political union, an alliance or an organisation.

   • We can secede from the United Kingdom any time we want. — 2007
2. •
   To split or to withdraw one or more constituent entities from membership of a political union, an alliance or an organisation.

   • At the same time, Nolan also secretly contracted with the crafty United States Army general James Wilkinson to organize some men to secede Texas from Spanish America. — 2002