The Manitoba was a case heard by the United States Supreme Court in 1887. The case involved a dispute between the United States and Canada over the ownership of a steamship called the Manitoba. The United States claimed that the Manitoba was owned by an American citizen, while Canada argued that the vessel was owned by a Canadian citizen. The Supreme Court ultimately sided with the United States, ruling that the vessel was owned by an American citizen. The Court held that the vessel was subject to the laws of the United States, and that the Canadian citizen had no legal right to the vessel. The Court also held that the vessel was subject to the jurisdiction of the United States, and that the Canadian citizen had no legal right to the vessel. The Court's decision was significant because it established the principle that vessels owned by American citizens are subject to the laws of the United States, regardless of where they are located. This decision has been cited in numerous cases since then, and has been used to support the principle that vessels owned by American citizens are subject to the laws of the United States.

The dissenting opinion in The Manitoba case argued that the majority had failed to consider the context of a treaty between two nations. In this case, it was an agreement between Great Britain and Canada concerning navigation rights on Lake Winnipeg. The dissent argued that while Congress had authority over foreign affairs, they could not unilaterally modify or abrogate a treaty without consent from both parties involved. Furthermore, since treaties are considered “the supreme law of the land” under Article VI of the Constitution, any action by Congress must be consistent with those terms. Therefore, if either party wishes to make changes to a treaty then both sides must agree before any modifications can take effect. As such, the dissent concluded that Congress did not have authority to pass legislation which would alter existing agreements made between other countries without their consent and thus should not be allowed in this instance either.