Oil Pirates, Nigeria

Piracy should be distinguished from privateering, which was authorized by their national authorities and therefore a legitimate form of war-like activity by non-state actors. This form of commerce raiding was outlawed by the Peace of Westphalia (1648) for signatories to those treaties.
Piracy is one of the offenses against which Congress is delegated power to enact penal legislation by the Constitution of the United States, along with treason and offenses against the law of nations. Treason is generally making war against one's own countrymen, and violations of the law of nations can include unjust war among other nationals or by governments against their own people.
Historically, offenders have usually been apprehended by military personnel and tried by military tribunals.
Some argue that the proper term for "terrorist" or "unlawful combatant" should be "pirate".