No other part of the 2nd Amendment induces more confusion and controversy than the phrase "well regulated militia". The online "debate" about gun control often results in dueling comments reading "SHALL NOT" vs "Well regulated militia"

But for a phrase that sits at the heart of the meaning of the 2nd Amendment, there's less popular discussion about what the "militia" in question actually meant when the Constitution was written, and why that matters

This phrase is largely ignored by those who oppose gun control, or if acknowledged at all, dismissed with spurious claims. And those who are pro-gun control generally focus on the "well regulated" part of the amendment

The word "militia" today largely conjures up one of two images - either armed Americans wearing camouflage running around in the woods, or groups of men with AK-47s and riding pickup trucks in Africa somewhere. It has a generally derogatory connotation, basically referring to an ad hoc, poorly organized military formation. But this is a far cry from what the term meant throughout American history - and understanding that history is crucial to understanding the reason why the writers of the constitution felt it necessary to write "A well regulated militia, being necessary to the security of a free state" in the part of the constitution that allegedly says the government can't regulate guns

If you want to read something by a professional historian and not a random dude on the internet, I highly recommend this article in American Heritage. If you want to read something that is more academic, I highly recommend googling the 2009 article "Pennsylvania, the Militia, and the Second Amendment", which can be found as a free PDF. Another great resource is a mini-history of the Watertown, MA militia

1. Colonial Origins

When the first British settlers established colonies in what is now the United States, they faced a problem - there weren't many of them, while there were large numbers of Native Americans. So local settlements and then entire colonial governments, using a system developed during the English Civil Wars, created Militia units. These were local forces composed of a large part of the male population, that regularly drilled (practiced). The goal was to provide a trained and organized military force that could rapidly be called into service to defend against Native American attacks, or more often, launch genocidal attacks against Native Americans. The exact composition of these militia varied by colony, mostly about the exact age range that would be called up, and whether black people could join, but all colonies had them.

It's important to note that these were organized military forces. Even the earliest militias which had individual soldiers bringing their weapons from home had officers, chains of command, were organized into companies, and regularly practiced. These were actual living and breathing organizations, not theoretical institutions on paper

2. The Revolutionary War

Even by the 1770s, the early colonial militia organizations had begun to atrophy. As Native Americans were killed or driven from many of the well settled parts of the colonial United States, the need to constantly practice and drill an armed force to prepare for native attack vastly reduced. Militias continued to exist and drill, but by the 1770s they had found a new reason to exist - war against the British. As tensions escalated between colonial leaders and the British government, these colonial militias started to take their role as organized military formations far more seriously. Remember, these were military organizations - and in the lead up to the war, these organizations stockpiled weapons and gunpowder, acquired heavier weapons, launched raids against British military institutions. The war that began at Lexington and Concord occurred after a British military formation attempted to capture or destroy a Massachusetts militia arms cache. Militia members brought their own arms to service often - but they also used government weapons, and the bullets and gunpowder that they fired came from Militia stocks and stores

Once war broke out, these militia served as the backbone of the American cause. These forces were available in large numbers, but problems soon emerged - these part-time soldiers, many of whom had even stopped regularly drilling, generally were not very good at their jobs. Being part-time soldiers, they were undisciplined, poorly trained if at all, they constantly got drunk, they did not like to serve outside of their home region, let along colony, and they were often unreliable in battle. George Washington's letters are full of complaints about this militia. But for all their complaints, militia units provided the bulk of American manpower in the war. And while the emphasis is often put on "minutemen" esque soldiers, many colonies even maintained a Naval Militia - an entire naval force under the command of a colonial military organization, not the official Continental Navy

3. The Constitution

After the war, with concerns that a domineering national government might overthrow state governments, the Continental Army and Continental Navy were largely disbanded - under the Articles of Confederation, the now renamed State Militia of each of the states provided America's military forces. When the Constitution was drafted, a significant concern of some of its drafters was that now that the US had a federal Army and Navy, this military force (the dreaded Standing Army of Jefferson's opprobrium) might be used by a tyrannical government to violate the rights of both US citizens and the individual states.

Enter the Militia. These advocates wanted to explicitly make it legal for the various states to be able to arm their state militias, with the thought that these state military forces could fight a war against a tyrannical federal government

Thus, here's why the 2nd Amendment contains the phrase A well regulated militia, being necessary to the security of a free state - to guarantee against potential Federal tyranny, enforced by the Federal US Army, states needed the right to maintain military forces independently of the Federal government

And indeed, after the Constitution, these state militias remained the backbone of the US Military. While the US Navy grew to respectable size, the US Army remained a tiny force, largely used to garrison the frontier and murder Native Americans - states were willing to pay for forts and armories to protect and arm their own citizens, but had no interest in maintaining forces in other states and territories. This proved very significant in the next war the US fought - the War of 1812. When the war broke out, there essentially was not a meaningful US Army - congress instead called up hundreds of thousands of State Militia and (with the consent of states) put them under federal command. These State Militia performed very poorly - they were essentially untrained, poorly armed, and were often reluctant to serve outside of their home state. When the US invaded Mexico, many of the military units raised were simply taken from the existing State Militias - though performed better, as they were trained before going into service

4. The Civil War and the end of the Colonial Militia system

Despite their poor performance, the State Militias continued to be the backbone of the US Military. States maintained large armories and arsenals, and had on-paper organized military units ready for mobilization in a time of war. The goal was again to provide a military force outside of the Federal government, and to allow the states to fight a war against a "tyrannical" government. And that is exactly what happened in 1861

The State Militias provided both the bulk of early forces in the Civil War, the weapons and military supplies that allowed the Confederate cause to establish itself, and they continued to exist as separate entities throughout the war. The first shots of the war were fired not by the Confederate Army, but by soldiers of the South Carolina Militia. The 75,000 volunteers that Lincoln called up to suppress the rebellion weren't just volunteers off the street, but were federalized regiments coming from the State Militia. Robert E Lee's first military command in the war was not in Confederate service, but as the head of the Virginia state military (including a State Navy). Pennsylvania was especially notable for maintaining a large independent military force - the Pennsylvania Reserves were an infantry division recruited and equipped at Pennsylvania state expense, with its officers appointed by the Pennsylvania Governor. The northernmost battle of the Civil War, fought at Sporting Hill in Pennsylvania, involved New York and Pennsylvania Militia - not US Army forces

With the eventual victory of the Union during the war, the Militia system was largely dismantled throughout the disarmed South - turns out that a system that allows individual states to maintain a private army to fight against the US Government isn't the greatest idea. The post-Civil War US had a much stronger Federal government, with state governments reduced in power

5. The Militia Act of 1903 and the creation of the modern National Guard

In 1898, the United States went to war with Spain. Though the US Navy had been built up to a significant degree, the US again faced the age old problem of "not having a meaningful army". The tiny force used mostly against Native Americans was not adequate to launch an expeditionary war overseas, and there was no functional system of reserves. Once again, the US turned to the remnants of the State Militia to outfit a brand new army, and once again the same problems cropped up - units were largely untrained, poorly equipped, or needed to be created from scratch entirely. Like the Mexican War, the US muddled through - but it was increasingly clear that this system was not working. Furthermore, unlike before the US now had an overseas empire to fight natives in and defend against European countries - the US needed a larger standing army, but more importantly, needed a system where part-time reserve forces could be called out on short notice and unlike with the previous militias, actually be well trained and equipped

The Militia Act of 1903 essentially federalized the State Militias and converted them into the modern National Guard. The money for these National Guard units would largely come from the Federal government, their training and equipment would be standardized at a federal level, and the rules for calling them into federal service would be clarified. This act was amended and changed over time, but the modern National Guard is the direct successor to the "well regulated militias" the 2nd Amendment mentions