The law of most of the states is based on the common law of England; the notable exception is Louisiana, whose civil law is largely based upon French and Spanish law. The passage of time has led to state courts and legislatures expanding, overruling, or modifying the common law; as a result, the laws of any given state invariably differ from the laws of its sister states. Thus, as noted above, the U.S. must be regarded as 50 "separate" systems of tort law, family law, property law, contract law, criminal law, and so on. (In addition, the District of Columbia and the federal territories also have their own separate legal systems analogous to state legal systems, although they do not enjoy state sovereignty.)