Europe has a long history of left-wing political violence, while in the United States political violence has been more likely to come from the right in recent decades, according to multiple studies

That second part is according to multiple studies, that first part is [citation needed].

I can't really think of any famous instances of left-wing violence in Europe in the last 100 years. The Years of Lead? But the deadliest attack during that time was by fascist terrorists.

The right screams bloody murder when a left-wing group blocks a highway for an hour. Meanwhile, right-wing groups are arrested for conspiracy to murder high profile politicians.