What significant legal power did the Supreme Court gain under John Marshall's leadership?

Under John Marshall's leadership, the Supreme Court gained the significant legal power of judicial review, which is the authority to interpret the Constitution and invalidate laws or government actions that are deemed unconstitutional. This power was established in the landmark case Marbury v. Madison in 1803, where Marshall asserted that it was the role of the judiciary to ensure that no law contradicted the Constitution.

Judicial review has become a foundational principle of American constitutional law, allowing the Supreme Court to check the powers of the legislative and executive branches, thereby maintaining the balance of power within the federal government. This function plays a crucial role in protecting individual rights and upholding the rule of law, making it one of the most important legacies of Marshall's tenure as Chief Justice.