From Makarska to Belgrade, there is bus connection year around, the bus travel via the Croatian and Serbian highway, the travel route has a length of almost 900 km.
By Car:If you travel by car you can choose to travel via Sarajevo, this route is only about 500 km, but do to road conditions it is not faster then the route which the bus drives.
By Plane: During summer season, it is possible to travel from Dubrovnik and Split to Belgrade
By Train: There is train from Ploce to Sarajevo, from there you can then continue by bus.