We do have laws against that, but terrorists dont fight for a nation, they are a murderous cult.
Then why is it a 'war on terror'? Why are soldiers involved if it's a cult? Why not police?
If soldiers are engaged and killing it is a war. If the president calls it a war it is a war. If you capture someone during that war they are a prisoner of war.
The only clever thing GWB ever did was not officially declare war on either Afghanistan or Iraq as a country therefore allowing any captured soldiers to be 'enemy combatants' and allowing the US to circumvent it's own laws and international laws to allow torture.
Another quick question the Taleban fighters that remain in gitmo, the ones who are Afghan citizens are 'enemy combatants' right? Well what about the northern alliance that fought with the US are they not enemy combatants too or is it okay for militia groups to join the war as long as they are on the US side?