Here is the full text of the 2nd Amendment:
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.
Joseph Story was professor of law at Harvard University and served as a Supreme Court Justice for thirty-five years.
The militia is the natural defence of a free country against sudden foreign invasions, domestic insurrections, and domestic usurpations of power by rulers. . . .
The right of the citizens to keep and bear arms has justly been considered, as the palladium of the liberties of a republic; since it offers a strong moral check against the usurpation and arbitrary power of rulers; and will generally, even if these are successful in the first instance, enable the people to resist and triumph over them.