In "An Occurrence at Owl Creek Bridge" what is the situation in the story? What did Farquhar do to deserve his execution?

The situation in this story is that the Union army has
invaded deep into the South.  They have gotten near to Farquhar's plantation.  He does
not like this and he wants to do something to fight back against
them.

What Farquhar does is to try to sabotage the bridge
that crosses Owl Creek.  According to the laws of war, it is illegal to try to commit
sabotage unless you are in the uniform of your country's armed forces.  Otherwise, you
are a spy and you are liable to be executed.

Of course, the
guy who egged Farquhar into doing it was committing an illegal act since he wasn't in
uniform, but he didn't get caught.