In the Douglas v. Wallace case of 1895, the U.S Supreme Court ruled on a dispute involving land ownership in California. The plaintiff, Mrs. Douglas, claimed that she was entitled to certain lands under Mexican law before California became part of the United States and argued that her rights were protected by the Treaty of Guadalupe Hidalgo which ended the Mexican-American War in 1848. However, defendant Mr. Wallace contended he had legal title to these lands based on subsequent American laws and regulations governing property rights in California after it joined as a state. The court held for Mr. Wallace stating that while Mrs.Douglas's claim might have been valid under Mexican law prior to 1848; however, once California became part of America all previous claims needed to be presented within two years according to an Act passed by Congress in March 1851 or they would be considered voided. This decision reinforced American sovereignty over former territories acquired from Mexico and established clear guidelines for resolving disputes over pre-existing land claims.

In the dissenting opinion for Douglas v. Wallace, Justice Brewer argued that the majority's decision to uphold a state law taxing out-of-state insurance companies was incorrect. He believed that this tax violated the Commerce Clause of the U.S. Constitution by placing an undue burden on interstate commerce. According to Justice Brewer, insurance is not merely a contract but also involves transactions and negotiations across state lines, which should be protected under federal law from discriminatory taxation by individual states. The justice contended that allowing such taxes could lead to protectionist measures and trade wars between states, undermining national unity and economic integration.