In the case of Muskrat v. United States in 1910, David and Joseph Muskrat, Cherokee Indians, challenged an act of Congress that allowed certain cases to be brought before U.S. courts for determination regarding the legality of allotments under a previous agreement with their tribe. The Supreme Court ruled against them stating that it had no jurisdiction over such matters as they were not actual controversies but rather contrived ones created by Congress for testing purposes only. This was because both parties (the plaintiffs and the government) essentially wanted the same outcome - validation of land titles - which meant there was no real dispute or adversity between them required for a justiciable controversy under Article III of Constitution. Therefore, this case established important precedent on what constitutes a "case" or "controversy" within federal judicial power.

In the dissenting opinion for Muskrat v. United States, Justice Harlan argued that the case was not a mere advisory opinion but rather an actual controversy between parties with adverse interests. He believed that Congress had authority to grant jurisdiction to federal courts over cases involving constitutional questions and disputes about congressional statutes, even if those disputes involved only declaratory judgments without any coercive relief sought by either party. Furthermore, he disagreed with the majority's interpretation of Article III of the Constitution as limiting judicial power solely to cases in which some immediate or threatened injury could be redressed by a court order; instead, he viewed it as encompassing all "cases" and "controversies," including ones seeking merely declaratory relief. In his view, this broader understanding better served both separation-of-powers principles (by allowing each branch of government its own sphere) and rule-of-law values (by ensuring legal certainty).