They are upgrading facilities in Belgrade to make it ATP500. They were then looking for options on where to host tournament this year and chose Banja Luka where majority of Serbians live even though it is in Bosnia. Bosnian history is complicated, they have regions where majority is either Croatian, Bosnian or Serbian. Anyway, Banja Luka was a long time challenger and in order to have it hosting ATP250 they had to build a stadium which is currently under construction and hopefully will be finished in time for the event.
This Banja Luka place is only 180 km away from where I live. I am thinking to go with my son. Wife said it's dad-son kind of event, good for bonding, in other words she doesn't watch tennis.