The Bill of Rights was not part of the original constitution but was later added as a compromise to ensure the constitution would be ratified by the required number of states. Do we know who wrote the second amendment? And do we know exactly why the "right to bear arms" was considered essential at the time. Was there s specific state or interested party pulling for this? Was there an opposition to it? I'm aware of the popular explanations, but is there more context to it than that simple narrative we so often hear (i.e. The British attempts to remove weapons from colonial subjects prior to the revolution)?
Here's a paper I found on the subject. http://www.constitution.org/2ll/2ndschol/89vand.pdf. Essentially, the author argues that the founding father's drew much of their beliefs on an armed citizenry from the experience of the English in the prior century. Both Federalist and Anti-Federalist party's were in agreement that a large, powerful government was to be feared, and that a standing army's existence was a means to maintain the power of an unpopular government. A "right to bear arms" was considered necessary to allow for the defense against threats in lieu of a professional army.