"Federal statutes impinging upon important state interests "cannot . . . be construed without regard to the implications of our dual system of government. . . . When the Federal Government takes over . . . local radiations in the vast network of our national economic enterprise and thereby radically readjusts the balance of state and national authority, those charged with the duty of legislating [must be] reasonably explicit." F. Frankfurter, Some Reflections on the Reading of Statutes, 47 Colum. L. Rev. 527, 539-540 (1947), quoted in Kelly v. Robinson,479 U.S. 36, 49-50 n. 11, 93 L. Ed. 2d 216, 107 S. Ct. 353 (1986). It is beyond question that an essential state interest is at issue here: we have said that "the general welfare of society is involved in the security of the titles to real estate" and the power to ensure that security "inheres in the very nature of [state] government." American Land Co. v. Zeiss,219 U.S. 47, 60, 55 L. Ed. 82, 31 S. Ct. 200 (1911)."BFP v. Resolution Trust Corporation, 114 S. Ct. 1757, 128 L. Ed. 2d 556 (1994).
In the legal system of the United States, preemption generally refers to the displacing effect that federal law will have on a conflicting or inconsistent state law. The Supremacy Clause (Article VI, section 2) of the United States Constitution states that The Laws of the United States, (which shall be made in Pursuance to the Constitution), shall be the supreme Law of the land. Thus, when there is a conflict between a state law and federal law, the federal law (subject to the Tenth Amendment and Fifth Amendment and other Constitutional Law) trumps – or "preempts" – the state law, according to this theory. The term is also sometimes used to refer to the displacing effect state laws might have on ordinances enacted by municipalities.Wikipedia
The term "preemption" is also used in federal statutes in the context of land, such as in the historic Preemption Act of 1841, which allowed settlers the opportunity to legally obtain title to land if a settler remained on a plot of land for a certain time. This article does not cover that legal use of the term.