Brothers in armed conflict: Why Dinamo Zagreb vs Hajduk Split is

After the break-up of Yugoslavia, Croatia's big two quickly settled into mutual loathing from the March 2007 issue of FourFourTwo

Hajduk Split training watched by 3,000 rowdy fans with flares and banners ahead of fierce derby against Dinamo Zagreb

Croatian hooligans vs. soccer mafia – DW – 06/24/2016

Hajduk Split v Dinamo Zagreb: Flares, fires, faith & football at Croatia's 'Eternal derby' - BBC Sport

The football match that started a WAR: 30 years on from Zvonimir Boban kicking a policeman

Three Croatian U-18 Football Stars Among World's Top 50 Wonderkids - Total Croatia

Hajduk Split vs Dinamo Zagreb: Croatia's Eternal Derby Dominated by Politics

yugoslavia Goalden Times

Dinamo Zagreb vs Hajduk Split: 5 Classic Clashes Between Croatia's Eternal Duo

Dinamo Zagreb official response to AEK's statement (translation in the comments) : r/soccer