What i meant by "oath to the constitution" is the US military doesn't pledge allegiance to an administration or ideology or region. Its only purpose is to uphold the constitution of the United States of America. That's why the military operates the same no matter which political party is in power. At the end of the day, its only purpose is to defend the constitution.

If the US didn't goto war to preserve the union then the US, as defined the US constitution, ceases to exist. There is no provision in the constitution laying out the right (or even the method) for secession.

> There is no provision in the constitution laying out

Sure there is. It is called the amendment process, and requires a supermajority vote.

Unless, you are going to claim that using the amendment process, officially, as laid out in the constitution is some treasonous act, that the military would stop.

(Funnily enough, I have see people make this silly argument! That it is unconstitutional to use the official constitutional amendment process, and is treason!)

I mean the tenth amendment would imply the decision to secede is up to the states. There's no prohibition on secession in the constitution and I think it was evidence to the states when they formed a union that their union was voluntary, not coerced. IMO the decision to block secession was a treasonous and seditious act by Lincoln, and he has a lot of blood on his hands.

Google US Civil War