I will note that the 10th amendment reserves powers to the states, and to the people.
The people is distinguished from the states. It is the same word used in the 1st and 2nd Amendment, which both describe rights not assigned to the states.
Pretending that a state alone can secede is thus contrary to the 10th Amendment, so obviously so that the southern states did not bother to file a case in federal court to have the SCOTUS rule on secession. As RE Lee said, secession war simply rebellion, and in the event, it failed on its merits.
I DON”T read it THAT way.
If the Tenth Amendment reserves to the People and the States those powers not clearly designated to the Federal Government by the Constitution, and the Constitution does not clearly FORBID secession, the States have that right.
As I POINTED OUT, several of the articles of incorporation by individual states of the Constitution, particularly Virginia’s and New York’s CLEARLY specify that the state reserves the right to withdraw from the Constitution should it feel its rights are infringed.
The fact that the Federal Government WHEN IT HAD JEFFERSON DAVIS in its power, REFUSED to try him for Treason indicates that there was serious fear that the Courts WOULD NOT consider him a Traitor as he was involved in exercising rights the Constitution clearly did not forbid.
See:
http://avalon.law.yale.edu/18th_century/ratva.asp
Read the FIRST PARAGRAPH CAREFULLY.
Since this ratification document was accepted, its terms were, by its acceptance, extended to all the other states which so ratified the Constitution.
New York State had a similar provision in its document of ratification and so did at least one other state.
There is no reason why a state cannot legally secede from the Union.