Has a citizenry as well armed as ours ever been overcome by a tyrannical government?
Good question. I suspect that we're pretty much off the chart in terms of how well-armed we are as citizens. When you factor in the number of veterans - many with recent combat experience - that are part of the picture, it's pretty clear why the government has been... hesitant.
Look for New York to be a test case. With over a million refusing to register their ARs, it will be interesting to see what happens. Frankly I think one or two home invasions looking for weapons might be enough to initiate organized resistance.