They are similar, but dissimilar.
Antifa-Socialists/Communists/Anarchists who need/want a Civil War so they can remake America. From what I've seen they are primarily white 20 somethings
KKK-Proud Boyz, et al. White supremacists who need/want a civil war so they can "return" America to the way it was (i.e. white protestants rule, everyone else kneels)
BLM-Black supremacists who want a race war they will win, allowing blacks to take over every aspect of government, and then put the white people "in their place"
Booger Boyz, loose groupings of right-wingers who believe we have strayed from the Constitution (especially 2A) and need a civil war to restore constitutional order.
1st 3 groupings are organized with outside funding (esp Antifa and BLM) the last group is still organizing and IMO not as big a threat as Antifa.