Slap,

What do you mean by "true modern examples"? I would classify right-wing separatists (Christian Identity, sovereign citizens, et al) as groups that would like to overthrow the United States government. Most of the left-wing groups, except radical environmentalists, are now defunct.

Given the size and diversity of the U.S., America has weathered crisis fairly well. Although there have been a number of violent attacks every year against soft targets, I think the most concerning recent episode was the Bundy Ranch standoff which was a direct challenge to federal authority. The combination of discontent and widespread availability of arms would seem to suggest more incidents like this would take place. Why not? What makes the U.S. successful in suppressing these kinds of movements?