The U.S. Constitution provided for a permanent navy, but it would not do the same for an army.
The Congress shall have Power To …raise and support Armies, but no Appropriation of Money to that Use shall be for a longer Term than two Years….
ARTICLE I, SECTION 8, CLAUSE 12
Raising an army was supposed to take a special legislative act and be limited in time to meet some crisis. Of course, even at the slower pace of the 18th century, in a time of crisis it could conceivably take too long to raise an army, so state militias were the first line of defense. The Constitution provided for this too.
The Congress shall have Power To…provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions; To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively, the Appointment of the Officers, and the Authority of training the Militia according to the discipline prescribed by Congress;
ARTICLE I, SECTION 8, CLAUSE 15-16
At the time, the states were vastly more divided than they are today, particularly on the issue of religion. The Congregationalists of Massachusetts, the Presbyterians of New Jersey, the Quakers of Pennsylvania, the Catholics of Maryland, the Anglicans of Virginia and the Baptists of the Carolinas did not trust some overarching federal government to control their militias. This is why the states maintained the right to appoint their own officers and the training of their own soldiers. They would not have submitted to anything like the National Guard that we have today.
They also had the responsibility for arming their own militias, and this was partly because the federal government sure as hell didn’t want to pay for the expense. In fact, after the Whiskey Rebellion broke out in 1791, Congress decided that they needed to codify how militias were to be used in the future. In the Militia Acts of 1792, Congress was clear that the responsibility for arming the militias lied not just with the states but with every male citizen.
Militia members, referred to as “every citizen, so enrolled and notified”, “…shall within six months thereafter, provide himself…” with a musket, bayonet and belt, two spare flints, a cartridge box with 24 bullets, and a knapsack. Men owning rifles were required to provide a powder horn, ¼ pound of gunpowder, 20 rifle balls, a shooting pouch, and a knapsack.
Now, we’re working a little outside of a strict chronology here, but it’s easy to see how the Second Amendment’s concern with a “well-regulated” militia fits in. How, for example, could a man provide his own musket if he was prevented from buying one?
So, on the one hand, the distrust of standing armies and of an overarching federal power led to the adoption of the Second Amendment, and state militias would remain under state control as much as possible during a federal muster. On the other hand, to make this practicable, the Congress soon concluded that every man must own a firearm. The Second Amendment only restricted what the federal legislature could prohibit, but the Militia Acts applied to the states and their citizens.