From What Hath God Wrought: The Transformation of America, 1815-1848 by Daniel Walker Howe:
Jeffersonians of the founding generation had reposed great confidence in the militia as an alternative to a standing army that could be used against the liberties of the people it supposedly protected.This militia, organized in each locality, consisted of all physically fit white males of military age, who would supply their own arms and donate as much of their time as necessary to keep in training and readiness when called upon to deal with insurrection or invasion. This was the “well regulated militia” postulated in the Second Amendment of the Bill of Rights and prescribed by the federal Militia Act of 1792.
The militia had proved ineffective on many occasions in both the Revolutionary War and the War of 1812 (George Washington never put much trust in it), but its gradual disappearance in the generation after 1815 had nothing to do with its military shortcomings.
The militia gradually ceased to function because most male citizens resented it as an imposition, and hated serving in it so much that they either refused to show up for the periodic musters and drills, or if they came made a mockery of the occasion. Since the men who defied the militia laws constituted the electorate, politicians dated not to coerce service. White male democracy could successfully defy the law, as squatters defied landlords or Indian treaties…. When the war with Mexico came in 1846, the administration made little use of the militia and relied instead on its small professional army plus volunteers trained and equipped at government expense [p. 491].
Now, 170 years later, we have the most powerful military and most heavily-armed police in the world, while sad, angry men, with a death wish for themselves and others, “serve” in the “militia”.