A find your hypothesis interesting but let’s discuss a few different possible causal mechanisms than your primary suggestion (and it is possible that this drop is some combination of causes):
1) You bring up the possibility that the threat of Islamic terrorism has lead to a substantial increase in security levels, so more terrorist incidents are stopped or never get off the ground. If this is the primary cause then I’d expect most of the drop off to occur after the first bombing of the WTC in the 1990s, and a heavy post-9/11 drop-off but your graph shows a drop-off staring before then but then shows the most clear cut drop-off in the mid 1990s, so this may be part of the effect. The fact that the drop-off rate doesn’t get massively faster after 9/11 possibly undermines this. I think your point is also a valid one which suggests this isn’t what is happening or at least is only a small factor of what is going.
2) The American political scene may in some ways simply be more civilized than it was in the 1960s and 1970s. True in many ways things at the congressional level feel more partisan, but it may be that the groups which felt like they had no options other than violence don’t feel that way as much because they have politicians who represent their interests. Both the far-right and the far-left have more elected politicians than they did in the 1960s, as do many racial minorities. In that context, it looks like one has avenues that are not violence for getting voices heard.
3) Part of the decrease may be due to the same effects (whatever they are, such as higher abortion rates, lower lead levels, better education) that have reduced violence levels in general. As violent crime has gone down, so has the type of violent crime we generally put in a separate category.
4) (Related to point 2) The internet gives people a feeling like they can get their voices heard with a feeling of (possibly illusionary) productivity, whether it is organizing boycotts or letter writing campaigns or simply venting to like-minded people.
Responding separately to your point about lone-wolf cases, part of the issue here may be classification. Many lone-wolves have ideologies or the like which they claim are motivating them, even if they have their own unique spin. It may be that we’re choosing to classify them as such rather than seeing them as part of their claimed ideologies. Also, it may be that lone-wolves are easier to be in the US since guns are more available whereas in many countries (especially in Europe and Japan) the lack of easily available firearms means that people need to cooperate in larger groups to get weapons.
A find your hypothesis interesting but let’s discuss a few different possible causal mechanisms than your primary suggestion (and it is possible that this drop is some combination of causes):
1) You bring up the possibility that the threat of Islamic terrorism has lead to a substantial increase in security levels, so more terrorist incidents are stopped or never get off the ground. If this is the primary cause then I’d expect most of the drop off to occur after the first bombing of the WTC in the 1990s, and a heavy post-9/11 drop-off but your graph shows a drop-off staring before then but then shows the most clear cut drop-off in the mid 1990s, so this may be part of the effect. The fact that the drop-off rate doesn’t get massively faster after 9/11 possibly undermines this. I think your point is also a valid one which suggests this isn’t what is happening or at least is only a small factor of what is going.
2) The American political scene may in some ways simply be more civilized than it was in the 1960s and 1970s. True in many ways things at the congressional level feel more partisan, but it may be that the groups which felt like they had no options other than violence don’t feel that way as much because they have politicians who represent their interests. Both the far-right and the far-left have more elected politicians than they did in the 1960s, as do many racial minorities. In that context, it looks like one has avenues that are not violence for getting voices heard.
3) Part of the decrease may be due to the same effects (whatever they are, such as higher abortion rates, lower lead levels, better education) that have reduced violence levels in general. As violent crime has gone down, so has the type of violent crime we generally put in a separate category.
4) (Related to point 2) The internet gives people a feeling like they can get their voices heard with a feeling of (possibly illusionary) productivity, whether it is organizing boycotts or letter writing campaigns or simply venting to like-minded people.
Responding separately to your point about lone-wolf cases, part of the issue here may be classification. Many lone-wolves have ideologies or the like which they claim are motivating them, even if they have their own unique spin. It may be that we’re choosing to classify them as such rather than seeing them as part of their claimed ideologies. Also, it may be that lone-wolves are easier to be in the US since guns are more available whereas in many countries (especially in Europe and Japan) the lack of easily available firearms means that people need to cooperate in larger groups to get weapons.