Football is a seriously tribal pursuit.
It arouses all the 'gang' mentality of the cerebrally challenged who need some of the basic affirmation they never received growing up, to assuage their deep-seated sense if isolation and insecurity.
The sense of a tribal camaraderie is supplied by joining fellow supporters in the chanting and mass back-slapping sense of 'belonging' that they get from football, add in being a small minority in a foreign country, and those feelings are heightened even further.
Also in play (!) is the primeval sense of fear and loathing of anyone who is 'different', and all that is required to set off that reaction is for fans of an opposing team to appear. Once again, add in the additional frisson of the other fans being 'foreign', and the hate/fear quotient increases once again.
And finally, take that mass of hormonal cod-masculinity with all its twisted ideas of 'honour' and 'brotherhood' and the desire for conflict and violence as a release of pent-up emotions they don't comprehend, and soak it in excess alcohol for several hours.
That eliminates any last vestiges of sensible mature adult behaviour that befits visitors to another country to enjoy a sporting event, and turns it into an excuse to inflict physical pain on complete strangers, and smash up the surroundings in ways they did as small boys invited round to play in a friend's garden, but never invited back.
Et voila - hooliganism.