From the Document: "The Second Amendment states that '[a] well-regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear arms, shall not be infringed.' Before the Supreme Court's 2008 opinion in 'District of Columbia v. Heller', the Second Amendment had received little Supreme Court attention and had been largely interpreted, at least by the lower federal courts, to be intertwined with military or militia use. Still, there had been ample debate in the lower federal courts and political discussion over whether the Second Amendment provides an individual right to keep and bear arms, versus a collective right belonging to the states to maintain militias. 'Pre-Heller', the vast majority of lower federal courts had embraced the collective right theory."
CRS Report for Congress, R44618
Congressional Research Service: https://crsreports.congress.gov/