The context of militias around the time of the writing of the Constitution was explained in the link that I provided. More on that in a second. My key point w

The context of militias around the time of the writing of the Constitution was explained in the link that I provided. More on that in a second. My key point was that there wasn't a right for a person...to keep and bear arms. There was a right for THE PEOPLE to do so as part of a militia. With two major points to be kept in mind. The first was that not all militias were government organized. The second was that this right was a protection from federal interference. For example Virginia didn't want Congress deciding to undermine how they ran their militia. Furthermore it is important to understand that the phrase "bear arms" at the time referred only to military service. Carrying your hunting rifle was not "bearing arms", and there are multiple court cases from that era affirming this understanding. Now back to militias. It varied by state and time period. The brief goes into some detail. But for existence at the time of the Revolution Virginia had a state regulated militia. Pennsylvania couldn't by its Constitution, but many local areas had their own militias. (For example towns would to defend against Indian attacks.) But in all cases, militias were set up so that the general citizenry would serve as an army in time of crisis for defense of the state or themselves. And this idea had a long history behind it.