https://archives.fbi.gov/archives/ne...-united-states
The FBI divides the terrorist threat facing the United States into two broad categories—domestic and international.
Domestic terrorism is the unlawful use, or threatened use, of violence by a group or individual based and operating entirely within the United States (or its territories) without foreign direction committed against persons or property to intimidate or coerce a government, the civilian population, or any segment thereof, in furtherance of political or social objectives.
During the past decade we have witnessed dramatic changes in the nature of the terrorist threat. In the 1990s, right-wing extremism overtook left-wing terrorism as the most dangerous domestic terrorist threat to the country. During the past several years, special interest extremism—as characterized by the Animal Liberation Front (ALF) and the Earth Liberation Front (ELF)—has emerged as a serious terrorist threat. The FBI estimates that ALF/ELF have committed approximately 600 criminal acts in the United States since 1996, resulting in damages in excess of 42 million dollars.
The second category of domestic terrorists, left-wing groups, generally profess a revolutionary socialist doctrine and view themselves as protectors of the people against the “dehumanizing effects” of capitalism and imperialism. They aim to bring about change in the United States and believe that this change can be realized through revolution rather than through the established political process. From the 1960s to the 1980s, leftist-oriented extremist groups posed the most serious domestic terrorist threat to the United States. In the 1980s, however, the fortunes of the leftist movement changed dramatically as law enforcement dismantled the infrastructure of many of these groups, and the fall of communism in Eastern Europe deprived the movement of its ideological foundation and patronage.....snip~
As noted the Specific interest terrorism mentioned are the most serious domestic threat in the US. What the FBI didnt mention is that these 2 groups are specifically Left Wing.