Croatia has a history of Nazism. Croatia was a Nazi puppet state once upon a time in WW2, with Pavelic at the helm. He was an Ustasa, Croatian nazis. Jasenovac was like the Auschwitz of Croatia. It was an extermination camp for Jews, Homosexuals, Gypsies and mostly Serbs.
Eventually, Tito's Partizans (Communists) was also a regime in Croatia, who'd fight the Ustase. Then you had neutrals, who just wanted to stay alive, not align themselves and watch over their families.
I can give a long ass history lesson about it, but I'll spare you and just say, there are racist/extreme fans in every country, many even worse. The Poles are psychos lol.
I would say for a lot of times, we don't start it. For example, when we beat Italy in Livorno right after the World Cup. Their fans were waving the Yugoslav/Croatian communist flag. If you know any Croat, that's one of the biggest insults you can throw at him. So, Armada fans from Rijeka who were at the match decided to make a human swastika. lol. Just to remind Italians, they're a bunch of shits also.
We got fined 30 000 Euros, the Italians got jack shit.
So you have a lot of these occasions where its just a retort. Then again, it depends on what firms attend matches, and their alignment.
It's a shame though, cause most of our fans are not extreme like that. We will sing for 90 mins straight till our lungs bleed without anything remotely racist. Like they say, a few rotten apples can spoil a bunch.