Let's take this at face value. The framers of the constitution did not want the populace stripped of the right to possesses and bear arms. They had recently freed the colonies of British rule, not with a powerful standing army, but with a loosely-organized and diffuse "army" consisting of citizens who had previously been required to fight on behalf of the Crown in Nova Scotia, upstate New York, Northern Massachusetts (Maine), and countless more focused spots where the British felt their interests were at peril. The point is that eventually, the colonists wanted self-determination and they fought for it. The framers of the constitution knew that no form of government was free of corruption, coercion, etc, and they included the 2nd amendment as a way to prevent despotic governments from gaining absolute authority.
I can tell you that if an invading force moved into Maine, the sheer number of accurate high-power deer rifles and experienced marksmen would make it very tough for them to hold this area. They might have a great time in areas in which rifles are impractical and handguns are banned, but they would not do well here. A couple of guys flanking a major road with decent guns could deny that road to the enemy, at least during daylight.
The imperialists value military overkill with vast ranks of troops massed with superior firepower. Insurgents value tactics, intelligent disposition of assets, and the allowance of discretion on the part of the combatants... when to shoot, what or who to shoot, when to take cover, when to go to ground. The British army and navy were dominant on the world stage before and after the US revolution, yet they were no match for our lighter, more flexible forces. Does Viet-Nam ring a bell? The 2nd amendment does not convey us "rights" that can be withdrawn - it spells out the relation of the populace to those who govern in not-so-subtle terms.