Introduction:
An unlawful combatant is a secret agent, saboteur or (at times) a fanatic who pursues an armed purpose outside the normally accepted laws of war. Not wearing the uniform of a sovereign state (as in spying) or not being under the authority power of an identifiable body are the principal reasons for a fighter to be classified as "illegal". By dissimilarity, uniformed soldiers who commend atrocities are tried for war crimes.
There are a lot of particular cases, as well, including those in current years of armed militants who are deemed not to enjoy protection of the Geneva Convention (GC) on the grounds that they are not part of any country which is a treaty signator. These people need not be accorded lawful combatant status according to the laws of war. Many Western advocates who oppose America's conduct in its "War on Terrorism" (after 9/11) advocate extension of combatant status to unlawful combatants, on various humanitarian, legal and political grounds. There is the humanitarian idea that everyone should get a fair trial.
There is the legal theory that the Geneva Convention automatically applies to all enemies of treaty signatories. There is the political idea that requiring America to extend GC protection to its detainees is good, because it will otherwise undermine its military strategy. The "Detaining Power" may choose to accord detained unlawful combatants the rights of prisoners of war as described in the Third Geneva Convention (GCIII), but is not required to do so.
Unlawful combatants may retain rights under the Fourth Geneva Convention in that they must be "treated with humanity and, in case of trial, shall not be deprived of the rights of fair and regular trial". (Other terms occasionally used include illegal combatant or unprivileged combatant.) The phrase "unlawful combatant" does not appear in GCIII........
