Article I, Section 8, Congress shall have the power:
Clause 15: To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions;
Clause 16: 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;Typically I meet with one of two angry reactions. One is to say that I am interpreting the Second Amendment to refer to government troops, not private citizens. The other is to say that it is precisely because the government has such a military that private citizens must be allowed to own guns -- to resist it.
But this takes a mistaken view of what the militia is. It starts out with the assumption that because the militia did not refer to regular troops, it must necessarily refer to every man and his gun with no formal military structure. When I offer the above quotes (to say nothing of the discussions at the Constitutional Convention), gun rights people assume that militia does mean regular troops and therefore that people outside the militia have the right to own guns in order to resist the militia. Unstated here is the assumption that there are civilians with guns and there are regular troops, that these are the only options, so that "militia" must refer to either one or the other. That assumption may be accurate in the US today, but it was not accurate in the 18th Century.
In fact, in the 18th Century, "militia" referred to a reserve military force that did, indeed, consist of every man and his gun. However, this militia was subject to military discipline. Its members lives as civilians most of the time, but periodically reported for training and drill. When they reported for training and drill, they formed into military companies, had officers (usually elected by the rank and file), and were subject to court martial and military penalties for breaches of discipline. During military emergencies (such as invasion, Indian attack, insurrection, etc), the militia would be called up by their government and operate under the command of their government. Israel and Switzerland still have such a system to this day. Such a system guarantees that the military cannot oppress the citizens because the military is the citizens.*
So why don't we have such a system today? Quite simply, because most people don't want it. Reporting periodically for militia drill and being called up in case of emergency was burdensome. Militia discipline was generally allowed to lapse because it was unpopular. The meaning of the Second Amendment is vague, but the reference to "a well-regulated militia" appears to suggest that it is in some way related to the sort of militia forces that existed in the 18th Century and do not exist today. What it means in the absence of such forces is anybody's guess.
Disclosure: I have been too lazy to do any serious research on 18th Century militia laws. (The fact that such laws existed at all refutes the argument that "well-regulated" had nothing to do with government control). I can offer this Wikipedia link for some basics.
*Non-citizens, like slaves or Indians in the US at the time of the Revolution, or Palestinians on the West Bank today, are a different matter.