A well regulated militia, being necessary to the security of a free state; and the right of the people to keep and bear arms, shall not be infringed. (2nd Amendment)
When those words were attached to the Bill of Rights the Founders had a very specific purpose in mind. It is not a coincidence that it was added second only to the freedom of speech, religion, and ability to assemble peaceably and freely. They understood that without the 2nd Amendment there was really no reason to have the 1st.