The 2nd Amendment

The 2nd Amendment is necessary for one reason: if the citizens of the United States decide their government has become a tyrannical force, the 2nd Amendment guarantees a revolution is possible. Our founders were wise enough to realize their creation could be subverted.

'A well regulated militia' doesn't mean uzis for all, but the right to maintain an armed citizenry ensures 'the security of a free state' (even with single-shot muskets).

Here's the text: 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.