In Mesa v. The United States, the Supreme Court addressed a dispute between Mexico and the United States over land in California that had been granted to Mexican citizens by Spanish authorities before 1821. At issue was whether or not these grants were valid under U.S. law after Mexico ceded its territory to the United States following the Mexican-American War of 1846-1848. The court held that while some of these grants may have been valid at one time, they no longer had any legal effect because they did not comply with U.S.-mandated requirements for granting public lands within its borders; thus, all such claims must be brought before Congress for consideration and resolution if necessary. This decision established an important precedent regarding how foreign governments' actions prior to their cession of territory are treated under American law going forward, as well as underscoring Congress's exclusive authority over matters related to public lands within U.S boundaries

In Mesa v. The United States, the Supreme Court was asked to decide whether a Mexican citizen who had been living in California since 1846 could be considered an American citizen and thus entitled to protection under the Treaty of Guadalupe Hidalgo. Justice Grier wrote a dissenting opinion arguing that while it is true that citizenship can be acquired by residence, this does not mean that all persons residing within the boundaries of the United States are citizens. He argued further that even if one were to assume for argument's sake that Mr. Mesa was indeed an American citizen, he would still not have any right or claim against the government because his rights as such did not arise until after he became a resident of California and therefore after his alleged treaty rights had already expired. In conclusion, Justice Grier asserted that no matter what one's status may have been at some point in time prior to becoming a resident of California, they cannot acquire any new rights or claims from treaties which predate their residency there.