There is a painting in the Art Institute of Chicago that almost no one stops to look at. Thomas Birch painted it sometime between 1806 and 1812, and he called it Capture of the Tripoli by the Enterprise. It commemorates a war that has been almost entirely forgotten — which is a pity, because that war contains the most important argument the United States ever made about the freedom of the seas. And that argument is more urgently relevant today than it has been in two centurie