Oil Pirates, Nigeria

Piracy is a war-like act committed by non-state actors (private parties not affiliated with any government) against parties of a different nationality, or against vessels of their own nationality at sea, and especially acts of robbery and/or criminal violence at sea. People who engage in these acts are called pirates.
The term can include acts committed on land, in the air, or in other major bodies of water or on a shore. It does not normally include crimes committed against persons traveling on the same vessel as the perpetrator (e.g. one passenger stealing from others on the same vessel). The term has been used to refer to raids across land borders by non-state agents.
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.