Welch v. Mandevill was a case heard by the United States Supreme Court in 1816. The dispute arose when William Welch, an inhabitant of Kentucky, sued John Mandeville for trespass and damages to his property after he had been ejected from it by force. Welch argued that he held title to the land under a grant from Virginia which predated Kentucky's statehood and thus should be recognized as valid despite being issued before Kentucky became part of the Union. The Supreme Court ultimately ruled in favor of Welch, finding that although states have exclusive jurisdiction over their own lands, they cannot interfere with grants made prior to their admission into the Union unless there is clear evidence that those grants were invalid or fraudulent at the time they were issued. This decision established important precedent regarding how states must respect pre-existing titles granted before statehood and provided greater protection for landowners against potential abuses of power by newly formed governments.

In Welch v. Mandevill, Chief Justice John Marshall delivered the dissenting opinion of the Supreme Court. He argued that a state court should not have jurisdiction over a case involving federal law and that it was unconstitutional for them to do so. Marshall believed that only Congress had the power to make laws concerning bankruptcy proceedings and any other matters related to commerce between states or with foreign nations; thus, he concluded that state courts could not exercise such authority in this instance. Furthermore, he noted how allowing state courts to interfere with federal law would lead to confusion and inconsistency among different jurisdictions as well as create potential conflicts between states’ rights and those of the national government. In conclusion, Marshall asserted his belief that only Congress has exclusive power over all cases arising under its own laws or treaties made by it with foreign countries—and no other body can supersede their authority in these matters.