One of the biggest cases the U.S. Supreme Court will decide this year involves the right to bear arms. But in the long run, its decision in McDonald v. Chicago may be far more important to America’s entrepreneurs. It all depends on whether the justices decide to revive a constitutional provision it has neglected for more than a century.

When it was ratified in 1868, the 14th Amendment added several revolutionary new provisions to the Constitution, barring states from violating the “privileges or immunities” of citizens, or taking anyone’s life, liberty or property without “due process of law,” or depriving people of the “equal protection of the laws.” But the first time it heard a case under that amendment — in the 1873 Slaughterhouse Cases — the Supreme Court basically erased the privileges or immunities clause, dramatically limiting the way the federal government would protect people against wrongful acts by state officials.