In De Groot v. United States, the Supreme Court ruled that a federal court could not review the decisions of military tribunals in cases involving civilians. The case arose when Peter de Groot was arrested by Union forces during the Civil War and tried before a military tribunal for treason against the United States. After being found guilty, he appealed to a federal district court for habeas corpus relief on grounds that his trial had been conducted without due process of law and with no opportunity to present evidence or witnesses in his defense. The district court dismissed his petition because it lacked jurisdiction over matters decided by military tribunals; however, de Groot then appealed this decision to the Supreme Court which affirmed it unanimously. In its ruling, Chief Justice Salmon P Chase wrote that "the power of Congress is exclusive" when deciding how civil trials should be conducted within its own territories and possessions during times of war or insurrection - meaning only Congress can decide whether such proceedings must comply with civilian legal standards or if they are subject solely to martial law regulations set forth by executive authority alone

In De Groot v. United States, the Supreme Court was tasked with determining whether a contract between two parties could be enforced by the federal government when one of those parties had died before it was completed. The majority opinion held that such contracts were not enforceable and thus dismissed the case. However, in his dissenting opinion Justice Field argued that if both parties had agreed to enter into a contract prior to either party's death then there should be no reason why it cannot still be enforced after their passing. He further noted that this would provide an incentive for people to honor their agreements even after they have passed away as well as ensure fairness in contractual disputes involving deceased individuals or entities. Ultimately, he concluded that allowing these types of contracts would benefit society at large and should therefore be recognized under law.