It's hard to point to what to examples of what has happened due to Americans being armed. Rather, we can point to what hasn't happened.
We've seen too many disarmed citizens of other countries marched off to their deaths. Tyrants know they will expect no resistance, so it's easy for a small number to murder a much larger number of people.
We've also seen instances, even in America, where local disasters leave our deputized police ineffective. Anarchy has a hard time making headway here when the local bad guy can be terminated instantly.
Finally, it's much easier to put up with the leftist hate and insanity when you realize they have no means of imposing their will by force of arms.
Our Second Ammendment is doing its job when it doesn't have to be used. It's a deterrent that every citizen has available.
Especially here in Indiana. Lifetime concealed carry, anyone?