Many historians agree that the primary reason for passing the Second Amendment was to prevent the need for the United States to have a professional standing army. At the time it was passed, it seems it was not intended to grant a right for private individuals to keep weapons for self-defense.
Then, how many times has the 2nd amendment been changed?
More than 1,400 Second Amendment challenges have been decided since District of Columbia v. Heller, the landmark 2008 case in which the Supreme Court established an individual right to keep a handgun at home (but also emphasized that the right is subject to various forms of regulation).