The Second Amendment "shows just how far the poison of slavery pervaded the Constitution. It was intended to protect slaveholders who used militias to keep a firm grip on their slaves. It wasn't meant to let individuals prevent federal tyranny. How could it? By training rifles or handguns on the Army, Navy and Air Force? 
It was meant to guarantee the legality of well-regulated militias to handle the states' internal problems, especially the problem of a large slave population."  
Garry Wills, Pulitzer Prize winning American historian.