We were British colonies protected by the British Navy. When the 13 colonies rebelled, they had virtually no navy.
So they did what other countries did as force multipliers of their navies: They hired pirates.
They "commissioned" pirates to prey on British shipping. In 1776, the Continental Congress began issuing Commissions of Letters of Marque and Reprisal, authorizing pirates to attack, seize, and steal the goods of British ships.
Once commissioned, the pirate was called a "privateer." Btw, by 1776, Britain had long used pirates as privateers to harass Spanish shipping and colonies, and the entire island of Jamaica was seized by the British from the Spanish with the help of commissioned pirates, like the infamous Captain Morgan.
During the Revolutionary War, on the high seas, for ship captains, crews and passengers, there was no difference between facing a pirate and a privateer. For the privateer, the big difference was that he had a safe port to return to in America with his "booty" and if he was captured by the British he was treated as a prisoner of war rather than as a criminal because of his commission letters.
Even the Revolutionary War "naval" hero John Paul Jones ("I have not begun to fight") was probably a pirate, and at least a privateer in the eyes of the British, having disgraced himself from British service in the West Indies by having killed two men on two different occasions and fled trial.
So while I'm as opposed to Somali pirates as the next person, I'm a bit amused by the (mis)use of history to puff up our outrage.
http://www.history.com/this-day-in-history.do?action=Article&id=451April 3, 1776
Congress authorizes privateers to attack British vessels
Because it lacked sufficient funds to build a strong navy, the Continental Congress gives privateers permission to attack any and all British ships on this day in 1776.
In a bill signed by John Hancock, its president, and dated April 3, 1776, the Continental Congress issued, “INSTRUCTIONS to the COMMANDERS of Private Ships or vessels of War, which shall have Commissions of Letters of Marque and Reprisal, authorizing them to make Captures of British Vessels and Cargoes.”
“Letters of Marque and Reprisal” were the official documents by which 18th-century governments commissioned private commercial ships, known as privateers, to act on their behalf, attacking ships carrying the flags of enemy nations. Any goods captured by the privateer were divided between the ship’s owner and the government that had issued the letter.
Congress informed American privateers on this day that, “YOU may, by Force of Arms, attack, subdue, and take all Ships and other Vessels belonging to the Inhabitants of Great Britain, on the high seas, or between high-water and low-water Marks, except Ships and Vessels bringing Persons who intend to settle and reside in the United Colonies, or bringing Arms, Ammunition or Warlike Stores to the said Colonies, for the Use of such Inhabitants thereof as are Friends to the American Cause, which you shall suffer to pass unmolested, the Commanders thereof permitting a peaceable Search, and giving satisfactory Information of the Contents of the Ladings, and Destinations of the Voyages.”