Question

Which document was the first to guarantee citizens the right to bear arms

Answer 1

The document would be The English Bill of Rights.
The Bill of Rights 1689 allowed citizens of England to 
 "have Arms for their Defence suitable to their Conditions and as allowed by Law" in order to stand up if the government became tyranny. (Second amendment of united states on the other hand, created in 1971)

Answer 2

The right to bear arms was first instituted in the U.S Constitution as the second amendment.