I googled rules of war and civilians and see alot of info on how armed forces are to treat civilians.
My question, however, is how civilians are allowed to act toward those they deem to be the enemy.
Hypothetical: Say the current so-called War on Terror evolves into a war that is clearly declared and legal. Say I’m walking down the street and see someone who I believe to be the enemy. What am I allowed to do to that person? What if I act in good faith but was wrong?
If it is clearly declared and legal, then a set of legislation explaining exactly what is legal will also be enacted by Congress.
Without that, there is no way to answer your question.
Maybe in GD people will want to blue-sky it.
As it stands, the general body of international treaties and conventions on war generally hold that persons engaging in combat are subject to the protection of said treaties and laws only if they are members of an organized and duly appointed armed forces. That generally means being a soldier - specifically, it usually means wearing a uniform, carrying identification that says you are a soldier, and carrying arms openly as the case might be (e.g. not pretending to be a civilian, or putting the Red Cross on a combat vehicle.)
The Geneva Conventions that define these boundaries do make some allowance for militia or civilians that arise to defend their territory in the case of an invasion of time does not allow them to, say, sew uniforms or print up military IDs and the like, but otherwise legal protection is still offered only if the laws of war are followed as far as is reasonably possible given the circumstances.
In the scenario you describe, you are essentially not allowed to do anything. It doesn’t sound as if the person is in the vanguard of an invading force; you seem to be describing “hey, I know that guy is a known terrorist.” The normal laws of the land apply to you, because you’re not a soldier. If he’s actually trying to blow up a Pizza Hut, the law allows you to use force to stop him no matter if there’s a war on or not. But if he’s just walking to the 7/11 to get some potato chips, you really aren’t a legal combatant and should call the FBI.
The Geneva Convention specifically protects as prisoners of war any civilians who spontaneously take up arms to resist an enemy force. So if the enemy were to capture you, under international law, you’re supposed to be treated well. This has nothing at all whatsoever to do with whether a war is declared or undeclared: the GC applies in cases of violent conflict of an international nature, lawful or not.
However, I do not know how domestic laws would apply to the situation. Of course civilians are allowed under domestic laws to defend their lives with deadly force; but I have no clue what exceptions to homicide laws are provided by statute or case law in the case of enemy invasion.
So, now there is a federal law against buying potato chips at 7/11 that the FBI would be interested in?
And correct me if I’m wrong, but I believe terrorism is generally considered to be a crime, so if someone is trying to blow up a Pizza Hut, the reason why you’re allowed to intervene with force is the same reason why you would be allowed to intervene if someone is trying to commit murder or robbery in front of your eyes. It doesn’t have anything to do with the actual lawful course of war.