This was Justice Scalia's most game-changing decision in his 30 years on the bench

Supreme Court Justice Antonin Scalia, who died Saturday at the age of 79, wrote many notable opinions and dissents during his 30 years on the bench.

But there is one case that stands out: Scalia’s 2008 majority decision in District of Columbia v. Heller, which struck down Washington, D.C.’s handgun ban and led to a slew of lawsuits questioning the constitutionality of gun control.

“It was the first Supreme Court decision to authoritatively interpret the Second Amendment. It is rare for [a] justice to write on a constitutional issue where there is no prior case law,” UCLA law professor Adam Winkler told Business Insider in an email message.

That landmark decision ruled the Second Amendment “protects an individual right to possess a firearm unconnected with service in a militia, and to use that arm for traditionally lawful purposes, such as self-defence within the home.”

Here’s what the Second Amendment says: “A well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed.”

Man legal scholars, when reading that amendment, might interpret the “right to possess a firearm” does not apply to ordinary civilians who aren’t in the military. Scalia, however, said the first part of the sentence — “a well regulated militia” — merely stated why it was important for the American people to be able to bear arms: It was important for Americans to have this right so they could have a well regulated militia.

Scalia argued that first clause didn’t “limit the scope” of the second part of the sentence — that the “right of the people to keep and bear arms, shall not be infringed.” Americans needed this right so they could have a well regulated militia, but even civilians were guaranteed the right to carry guns, according to Scalia.

Scalia’s interpretation gave “life to the Second Amendment,” Carter Phillips, who’s argued dozens of cases before the Supreme Court, told Business Insider in an email message.

“It was his clearest win for his method of constitutional interpretation,” Phillips added, “and the consequences of the decision are profound.”

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