▁groups ▁have ▁long ▁existed ▁in ▁the ▁region , ▁and ▁there ▁has ▁been ▁a ▁strong ▁correlation ▁between ▁eth nic ▁identity ▁and ▁religious ▁affili ation , ▁with ▁Cro ats ▁being ▁mainly ▁Catholic , ▁and ▁more ▁Western - orient ed , ▁while ▁the ▁Ser bs ▁are ▁Eastern ▁Orth odox . ▁ ▁Following ▁the ▁dissol ution ▁of ▁the ▁H abs burg ▁Empire ▁at ▁the ▁close ▁of ▁World ▁War ▁I , ▁the ▁desire ▁of ▁Cro at ian ▁national ists ▁for ▁independence ▁was ▁not ▁real ised , ▁and ▁the ▁region ▁found ▁itself ▁first ▁in ▁the ▁Ser b - domin ated ▁Kingdom ▁of ▁Ser bs , ▁Cro ats ▁and ▁Sloven es , ▁and ▁then ▁in ▁the ▁equally ▁Ser b - domin ated ▁dict ator ship ▁of ▁Y ug oslav ia ▁established ▁by ▁King ▁Alexander ▁in ▁ 1 9 2 9 . ▁In ternal ▁borders ▁were ▁red ra wn ▁div iding ▁historical ▁Cro atia ▁into ▁several ▁provinces . ▁Political ▁repr ession ▁b red ▁extrem ism , ▁and ▁the ▁" U sta š a " ▁(" In s urg ence ") ▁was ▁formed ▁in ▁ 1 9 2 9 ▁by ▁An te ▁Pav eli ć , ▁with ▁the ▁support ▁of ▁F asc ist ▁Italy . ▁In ▁ 1 9 3 4 , ▁King ▁Alexander ▁was ▁assass in ated ▁by ▁a ▁Bulgar ian ▁gun man , ▁a ▁member ▁of ▁the ▁In ternal ▁Mac ed onian ▁Revolution ary ▁Organ ization , ▁a ▁radical ▁group ▁seeking ▁independence , ▁al lied ▁with ▁the ▁Cro at ian ▁U sta še ▁group ▁led ▁by ▁Pav eli ć .