Vietnam and the current war on terrorism are horrible examples for guerrilla warfare, both situations are tied back by the home populace and politics. Vietnam is a great example, it was almost won from a military standpoint, yet the civilian populace at home lacked in support. The current GWoT is another example of home politics influencing military doctrine, it is looser for cops than it was over there.
That doesn't include a duty to disobey, and the usual politics of individuals troops, which for some people are surprised to learn they aren't eager to invade Kentucky for example.
That's not to mention foreign intervention.