Ware v. United States was a United States Supreme Court case that was decided in 1866. The case involved a dispute between the United States and a private citizen, William Ware, over the ownership of a parcel of land in the state of Mississippi. Ware had purchased the land from the Choctaw Indians in 1859, but the United States claimed that the land had been illegally obtained and that it belonged to the United States. The Supreme Court ruled in favor of the United States, finding that the land had been illegally obtained and that the United States had a valid claim to it. The Court held that the United States had a right to reclaim the land, as it had been obtained in violation of the Treaty of Dancing Rabbit Creek, which had been signed between the United States and the Choctaw Indians in 1830. The Court also held that the United States had a right to reclaim the land even if it had been purchased in good faith by Ware. The decision in Ware v. United States established the principle that the United States has a right to reclaim land that has been illegally obtained, even if it has been purchased in good faith by a private citizen. This principle has been applied in numerous cases since then, and it remains an important part of the law today.

In Ware v. United States, the Supreme Court was tasked with determining whether a contract between two parties could be enforced when one of those parties had been acting as an agent for the government. The majority opinion held that such contracts were not enforceable because it would create a conflict of interest and undermine public policy. Justice Field dissented from this decision, arguing that while there may have been some impropriety in allowing agents to enter into private contracts on behalf of the government, enforcing these agreements should still be allowed if they are found to be fair and reasonable under all circumstances. He argued that denying enforcement would lead to injustice by punishing innocent third-parties who relied upon these agreements in good faith without knowledge or suspicion of any wrongdoing on either side. Furthermore, he noted that refusing to enforce such contracts could also lead to increased litigation costs due to disputes over their validity which would ultimately burden taxpayers unnecessarily.