In the 2010 landmark case McDonald v. Chicago, the Supreme Court declared the Second Amendment is incorporated through the Due Process Clause. However, Justice Thomas, the fifth justice in the majority, criticized substantive due process and declared instead that he reached the same incorporation only through the Privileges or Immunities Clause. No other justice attempted to question his rationale. This is considered by some as a "revival" of the Privileges or Immunities Clause.
In 1833 the US Supreme Court decided in Barron v Baltimore that the states could violate the Bill of Rights, because the Bill of Rights only restrained the federal government. After the civil war, the 14th Amendment was passed to protect the rights of blacks and former slaves from violation by state governments. But in seeming defiance of the plain meaning of the 14th Amendment, the Supreme Court decided in the Slaughter-House Cases, that the 14th Amendment only protected the "privileges and immunities" of US citizens against state violations, not their rights. The courts are very reluctant to overturn their prior rulings, but finally in the early 20th century, the Supreme Court came up with a way to get around their Slaughter-House rulings without expressly overturning themselves. In the case of Gitlow v. New York, they declared that the 14th Amendment prohibited the states from violating some of the rights of citizens without "due process". But the court stopped short of "incorporating" all of the bill of rights at once. Instead each amendment or even part of an amendment, had to be incorporated by the court individually. The Second Amendment was the last right in the Bill of Rights to be incorporated and was done so through McDonald v. Chicago in June 2010 .