Armour v. Hahn was a United States Supreme Court case that dealt with the issue of whether a contract between two parties was valid. The case involved two parties, Armour and Hahn, who had entered into a contract for the sale of a piece of land. Armour had agreed to pay Hahn a certain amount of money for the land, but Hahn refused to accept the payment. Armour then sued Hahn for breach of contract. The Supreme Court held that the contract between Armour and Hahn was valid and enforceable. The Court found that the contract was supported by consideration, meaning that both parties had given something of value in exchange for the land. The Court also found that the contract was not void for lack of mutuality, meaning that both parties had agreed to the same terms and conditions. The Court also held that Hahn was liable for breach of contract because he had refused to accept the payment from Armour. The Court found that Hahn had acted in bad faith by refusing to accept the payment and that he was therefore liable for damages. In conclusion, the Supreme Court held that the contract between Armour and Hahn was valid and enforceable and that Hahn was liable for breach of contract. The Court's decision established that contracts must be supported by consideration and that parties must act in good faith when entering into contracts.

In Armour v. Hahn, the Supreme Court was asked to decide whether a state court had jurisdiction over a case involving two citizens of different states. The majority opinion held that the state court did have jurisdiction in this case, but Justice Field dissented from this decision. He argued that under Article III of the Constitution and Section 2 of the Judiciary Act of 1789, only federal courts could hear cases between citizens from different states when more than $500 was at stake. Furthermore, he argued that allowing state courts to hear such cases would be an unconstitutional extension of their power since it is not explicitly granted by either document. In his view, Congress should pass legislation granting such authority if they wish for it to exist; otherwise any attempt by a state court to do so would be invalid and void as being beyond its constitutional powers