There is an interesting section that goes into the scholarly interpretation of the 2nd amendment in the Wikipedia article on it, and it's only been in the 20th century and after that we have gotten into what militia, well regulated and whether or not the people have the right or militias.

The main point the founding fathers had for the militias was to defend the country from foreign invaders and from a tyrannical government. I know people think we don't need to worry about tyrannical governments these days, but what if what happened in Libya, Syria and Egypt started happening here? How would we fix that kind of a situation?