First bursting into the headlines when they shut down far-right provocateur Milo Yiannopoulos in February at the University of California at Berkeley, antifascists again captivated the public imagination by battling the fascists assembled at the “Unite the Right” white power rally in Charlottesville. But what is antifa? Where did it come from? Militant anti-fascist or “antifa” (pronounced ANtifa) is a radical pan-leftist politics of social revolution applied to fighting the far right. Its adherents are predominantly communists, socialists and anarchists who reject turning to the police or the state to halt the advance of white supremacy. Instead they advocate popular...