In the case of AINSA v. UNITED STATES, 1895, the U.S Supreme Court was tasked with determining whether a land grant issued by Spain to an individual in Arizona before it became part of United States territory should be recognized under American law. The plaintiff, Ainsa, claimed ownership over a large tract of land based on this Spanish grant and sought validation from the court. However, after examining historical documents and treaties between Spain and Mexico (which had control over Arizona prior to US acquisition), as well as those between Mexico and the United States following its annexation of Arizona during Mexican-American War in 1848; the court ruled against Ainsa's claim. It held that while such grants were generally respected under international law principles when territories changed hands through conquest or treaty; in this specific instance there was insufficient evidence to prove that such a grant ever existed or if it did exist then it wasn't properly validated according to stipulations laid out within Treaty of Guadalupe Hidalgo which ended Mexican-American war.

In the dissenting opinion for AINSA v. UNITED STATES, 1895, Justice Brewer argued that the majority's decision was a misinterpretation of the Treaty of Guadalupe Hidalgo and its implications on property rights. He contended that under this treaty, which ended the Mexican-American War in 1848, land grants made by Mexico before it ceded territory to America were valid and should be recognized by U.S law. Therefore, he believed that Ainsa’s claim to his family's land grant from Mexico should have been upheld rather than dismissed as per majority ruling. The justice also expressed concern over potential negative impacts on other similar cases involving Spanish or Mexican land grants if such claims were not honored according to international treaties.