I’m working on a story idea, but ran into a lack of knowledge problem.

The story is about the a state, some fifteen years from now, trying to leave from the United States. They want to remain friendly with the rest of the states, but will no longer supply men, money, weapons, nor supplies of war to the US military.
Now, my knowledge of the national Guard stems from Civil War history, where the Guard were basicly state militias, under command of the state in which they came from.
So, my idea was that the National Guard of this particular state would be, or try to, withdraw from the nation’s service, and be brought up to protect the state itself when the US tries to take back the state.

(please note that this is a work of pure fiction intended for many years from now.)

I need to know how the politics of the National Guard works.
Is the National Guard like state militias?
How do the orders come down to the individual state’s Guard?
Who do the orders come through?
Does the state have some influence over the Guard’s orders?

Any information will be very helpful. Even if it means I have to rethink the story.

Thanks a bunch.
- The Chronicler