> Imagine the civil war if the union couldn't kill confederates.

A full scale civil war really is an extraordinary case and is a lot more akin to a regular war than what we are talking about here.

I'm more afraid of someone declaring war on an abstract concept (like the "war on terror") and then using broad powers meant to be used in normal wars between states that have declared combatants than I am of a civil war.

I wonder how that would play out in today's Congress. There is technically no country to declare war on, unless you can declare war on yourself, so they would have to first redefine the United States as two parts. After that is passed, they could declare war on the opposing half. I guess I'm kind of seeing how the Chinese governments got themselves tied up in knots with their continuity of state and all.

I'd imagine that you can declare war on a specific group (that does not have to be defined as a state) like the "confederate states of america" without it having to be a nebulous concept like "terror". But I don't know enough to say for certain.

If we have a declared war between the US and the people (US citizens or otherwise) who are taking up arms against the US, then sure, attack away.

But otherwise, the only remedy should be judicial process against these people: arrests, trial, etc. Otherwise we have a term for it: extrajudicial killing.

Of course, Congress has given the executive branch weird war powers over the past few decades, so legally I'm sure they're in the clear, unfortunately.