Here's how the Heritage Foundation sees it;
"The Founding generation understood that large standing armies were dangerous threats to liberty, especially when controlled by authoritarian governments who sought to disarm the general population. The militia system, with deep roots in English history, was one way of ensuring that the nation could defend itself against all threats, foreign and domestic. Instead of a large full-time professional army, the government could, when needed, call upon the greater body of armed citizens to employ their personal firearms in the collective defense of the state or nation. A “well-regulated” militia simply meant that the processes for activating, training, and deploying the militia in official service should be efficient and orderly, and that the militia itself should be capable of competently executing battlefield operations."
One good example of a poorly regulated militia, was the Whiskey Rebellion of 1794.. It seems congress passed an excise tax on whiskey, which was
especially punishing on those distillers in the hinterlands, greatly irritating those of the Appalachains in western Pennsylvania..
These farmers (grain growers) and distillers were soon "up in arms". A grass roots militia formed and raised havoc, until Pres Washington sent
in federal troops; the president himself, leading a portion of them as far as Bedford..near the neighborhood of his experiences during the French & Indian war.
The rebellion was put down, but it was rather just anger and the hap-hazard, quickly formed, militia (IMO) soon dispersed.
