My understanding of the Italian political climate of the 60s, 70s, and 80s is that there were political groups/cells (on both the far right and far left) that organized around violent acts to further their political goals (which involved the eventual authoritarian takeover of the Italian government by either the far right or far left). For example, you can think of the Red Brigades to be akin to the Black Panthers, but with actual terrorism.
In contrast, most political violence in America has been less organized and more individual-driven (e.g., see the Oklahoma City Bombing). For better or worse, the police state in the US has been quite successful in addressing and dispersing political groups that advocate for violence as a viable means for societal change.
Resistance orgs across the ideological spectrum were systematically dismantled after decades of violence because their hierarchical command structures made them vulnerable to infiltration, decapitation and RICO-style prosecutions.
The Weather Underground, Red Army Faction, European Fascist groups and many white supremacist groups all fell to the same structural weaknesses.
Lessons were codified by the KKK and Aryan Nations movements in the USA in the early 90s by Louis Beam[1] who wrote about distributed organisational models.
This was so successful it cross-pollinated to other groups globally. Other movements adopted variations of this structure, from modern far-right and far-left groups to jihadist organisations[2]
This is probably the most significant adaptation in ideological warfare since guerilla doctorine. There has been a large-scale failure in adapting to it.
The internet and social media have just accelerated its effectiveness.
"Inspired by" vs "carried out by" ideological violence today is the norm.
[0] https://en.wikipedia.org/wiki/Leaderless_resistance
[1] https://www.splcenter.org/resources/extremist-files/louis-be...
[2] https://www.memri.org/reports/al-qaeda-military-strategist-a...