The Constitution provides that it, as well as federal laws and treaties that are made pursuant to it, preempt conflicting state and territorial laws in the 50 U.S. states and in the territories.[6] However, the scope of federal preemption is limited because the scope of federal power is not universal. In the dual sovereign[7] system of American federalism (actually tripartite[8] because of the presence of Indian reservations), states are the plenarysovereigns, each with their own constitution, while the federal sovereign possesses only the limited supreme authority enumerated in the Constitution.[9] Indeed, states may grant their citizens broader rights than the federal Constitution as long as they do not infringe on any federal constitutional rights.[10][11] Thus U.S. law (especially the actual "living law" of contract, tort, property, criminal, and family law experienced by the majority of citizens on a day-to-day basis) consists primarily of state law, which can and does vary greatly from one state to the next.[12][13]
At both the federal and state levels, with the exception of the legal system of Louisiana, the law of the United States is largely derived from the common law system of English law, which was in force in British America at the time of the American Revolutionary War.[14][15] However, American law has diverged greatly from its English ancestor both in terms of substance and procedure[16] and has incorporated a number of civil law innovations.
^Hughes, Graham (1996). "Common Law Systems". In Morrison, Alan B. (ed.). Fundamentals of American Law. Oxford: Oxford University Press. pp. 9–26. ISBN9780198764052. Retrieved August 11, 2020.
^Hughes, Graham (1996). "Common Law Systems". In Morrison, Alan B. (ed.). Fundamentals of American Law. Oxford: Oxford University Press. pp. 9–26. ISBN9780198764052. Retrieved August 11, 2020.
^Friedman, Lawrence M. (2019). A History of American Law (4th ed.). Oxford: Oxford University Press. p. 3. ISBN9780190070915. Retrieved August 11, 2020. Professor Friedman points out that English law itself was never completely uniform across England prior to the 20th century. The result was that the colonists recreated the legal diversity of English law in the American colonies.