As James Madison noted in Federalist 46, the freedom to keep and bear arms is a safeguard against tyranny:
Notwithstanding the military establishments in the several kingdoms of Europe, which are carried as far as the public resources will bear, the governments are afraid to trust the people with arms. And it is not certain, that with this aid alone they would not be able to shake off their yokes. But were the people to possess the additional advantages of local governments chosen by themselves, who could collect the national will and direct the national force, and of officers appointed out of the militia, by these governments, and attached both to them and to the militia, it may be affirmed with the greatest assurance, that the throne of every tyranny in Europe would be speedily overturned in spite of the legions which surround it. Let us not insult the free and gallant citizens of America with the suspicion, that they would be less able to defend the rights of which they would be in actual possession, than the debased subjects of arbitrary power would be to rescue theirs from the hands of their oppressors. Let us rather no longer insult them with the supposition that they can ever reduce themselves to the necessity of making the experiment, by a blind and tame submission to the long train of insidious measures which must precede and produce it.
The principle of a subjugated people being disarmed is a well worn one. You can even see it in the Bible where early in the monarchy only Saul and Jonathan are allowed to have swords by the Philistines, and even blacksmiths seem to be prohibited among the Israelites.