Link: https://en.wikipedia.org/wiki/Antifaschistische_Aktion
Given the history that the communist Soviet Union was our ally in World War II, and fought on our side together in the Allied Forces against Nazi Germany, I would say Nazi and its successor neo-Nazi, - whose ideology is White nationalism and White supremacy, was and still is the bigger threat than Antifa.
So, Antifa and Nazi have always been archenemies. Antifa and Nazi exist like the two opposing sides of the Force, Light and Dark. When the Dark Side (i.e., Nazi) rises again, the Light Side (Antifa) also reemerges to fight. And Antifa has always used violence to fight against Nazi, and there is absolutely nothing wrong with Antifa's use of violence in fighting Nazi.
So, Antifa has reemerged only because the other side, the Dark Side, the true evil, has returned and become stronger.
This is insane. The "neo-nazis" are few and hold almost not political power. But places like CNN shilled for the authoritarian left Ati-fa (who, btw, represent an ideology far worse than the Nazis based on number killed). Many are anarco-commuinists. We didn't fight with them at all, and we have ALWAYS stood against authoritarian ideologies. Don't paint them for what they aren't. There is a reason they have been classified as a terrorist organization since 2016 internally.