[regular.joe]

The Army traces its heritage to the colonial militias. These were precursors of today’s Army National Guard. Citizens answering the call to protect their homes and families began a heritage of selfless service and sacrifice that continues today. Opposition to British colonial policies in the eighteenth century led to war in 1775.
After the battles at Lexington and Concord, militia forces from across New England surrounded British forces in Boston. The Continental Congress assumed command of these units as “Troops of the United Provinces of North America” on 14 June 1775.

from the start, the Army comprised a small national force and the state militias’ citizen-Soldiers. In times of emergency, the standing army was enlarged with recruits and augmented by mobilizing the militia and creating volunteer units, initially by state and nationally by the time of the Civil War. This tradition of an Army that combines “full-time” regular Soldiers and citizen-Soldiers serving for short active service periods is still the cornerstone of Army organization.

-FM 1 United States Army

yes the 2nd amendment was tied to the idea of having armed citizens in the United States, in militias, and not. Militias in those days could not be formed unless the citizens were privately armed. You are right to see a connection between the militia and the Military. The second amendment was not written to create this connection. This connection was started 14+ years earlier in our history.