As the line between privateering and piracy is often hard to draw, any act of doubtful legality committed on the seas is apt to be characterized as piracy. Thus the sinking of merchant vessels by the Germans in World War I was characterized by some as piracy, although the act was done on the authority of a national state. However, at the Washington Conference of 1921 a treaty was concluded that declared that improper visit and search (see search, right of) by one in the service of any power would constitute piracy.
Since piracy is a crime against humanity, those practicing it may be tried in any competent court, regardless of nationality. To the forms of piracy defined by international law, however, a nation may add offenses committed on board its own vessels or in its own territorial waters.