The New York Legislature had passed a law giving a monopoly on steamship travel in New York state to a group of investors. Among the people who had permission to do this monopoly was Aaron Ogden. Thomas Gibbons, another steamship trader, wanted to use the New York waterways for his business but was denied access. Gibbons sued Ogden.
they said that the U.S. Constitution had a commerce clause that allowed the federal government to regulate commerce, in this case trade, wherever it might be, including within the borders of a state the Supreme Court extended the definition of interstate commerce.
the Supreme Court extended the definition of interstate commerce and cemented the power of the federal government over the states when the laws conflicted.