The most often quoted reason for the existence of the 2nd Amendment is self-protection. Makse sense. At that time, Indian attacks were still a possibility, people lived on remote farms and there were no established police forces in every city and town.
A lesser cited reason is defense against a tyrannical government. If you have studied world history leading up to the Revolutionary War, you could see where this may have been the main reason for the 2nd Amendment.
But does this make sense in the 21st Century? Critics of the 2nd Amendment will tell you it is ridiculous to think that small bands of American citizens armed with hunting rifles and revolvers could stand against the most modern army in the world. An Army armed with tanks, artillery and armored personnel carriers supported by an Air Force with bombers, jet fighters and drones. How could mere citizens stand against a force so heavily armed? It’s impossible, right?
Not only is it possible, it has happened in the past and is happening today. For ten years, 1979-1989, the most heavily armed force in the world (Soviet Union) was fought to a stalemate by small groups of men with rifles. The Soviet Union eventually withdrew in defeat.
If a well-trained, heavily armed force can easily defeat a lightly armed, untrained force, why is ISIS still a threat? Why haven’t they been bombed into oblivion?
If you don’t believe our government could ever get so oppressive that men would take up arms against it, look at where we are already: the NSA is listening to phone calls, the government wants to control the internet, the government forces you to buy health insurance “for your own good”, the DEA proposed using license plate readers at gun shows to track everyone that attends the show, the IRS is attacking “enemies of the State”, the EPA “declares” thousands of acres as wetlands falling under their control, the Department of the Interior decides where cows can graze, in Maryland, you can be fined if there is too much sediment in the rainwater that runs off of your property, and the list goes on.