“Bandera is our father, Ukraine is the mother. We will fight for Ukraine!” sings a young woman in camouflage, carrying a submachine gun, in a video that Ukrainian Mariupol defenders shared on social media in early May. The video appears to have been recorded in a bunker at the Azovstal Steelworks, the city’s last bastion for Ukrainian resistance to Russian troops. “Azov” fighters were also there, a regiment founded by radical nationalists which was later placed under the supervision of the Ukrainian Ministry of the Interior. Stepan Bandera, killed by Soviet intelligence agents in West Germany more than 60 years...