the modern day national guard in the united states traces its origins to 13 december 1636, when the massachusetts bay colony's general court passed an act calling for the creation of three regiments, organizing existing separate militia companies in and around boston. the creation of the militia regiments was caused by the perceived need to defend the bay colony against american indians and from other european countries operating in north america. this organization formed the basis of subsequent colonial and, post-independence, state and territorial militias which later became the army national guard.