If ND, SD, Nebraska, Kansas, OK and Texas seceded all at once they could cut the country in half. So what? Ukraine does not have to secede from Russia, it is already its own country. Russia is trying to get it back by force.
Ok, if you house gets totally encircled and there are no easments the people who own all the land that encircled your house own you.
States should not own other states so seccession by a group of states to encirle and thereby own another state should not be legal.