From Bearing Arms:

After analyzing these interpretive similarities, this research makes the following contentions: the original public meaning of the Second Amendment indicated an understanding of both an individual right to keep and bear arms as well as a declarative statement on the militia that had no limiting effect on the individual right. Put another way, the first clause (the Militia Clause) does not create a condition for the second clause. Instead, it declares an axiom as understood by the framers: a well-established and well-outfitted militia (broadly defined as the entirety of the national populace) is necessary to securing a free nation. To support this dictum, the amendment subsequently recognizes the individual right to keep and bear private arms, because the militia is made possible by private arms rather than the other way around. With the publication of the Bill of Rights, the Constitution endorsed an armed citizenry as the best possible defense of a nation’s liberties rather than making the individual ownership contingent on the continued use of a militia.