▁principal ities ▁were ▁absor bed ▁into ▁a ▁central ised ▁political ▁structure ▁and ▁these ▁ind igen ous ▁el ites ▁were ▁included ▁in ▁the ▁administration ▁( which ▁they ▁shared ▁with ▁the ▁Dutch ▁) ▁of ▁the ▁region . ▁Con sequently , ▁both ▁the ▁Dutch ▁and ▁Mal ay ▁arist ocr ats ▁were ▁able ▁to ▁use ▁their ▁political ▁power ▁to ▁launch ▁policies ▁that ▁suppress ed ▁the ▁rights ▁of ▁the ▁common ers . ▁O pp osition ▁to ▁the ▁Dutch ▁repr ession ▁and ▁Mal ay ▁arist ocracy ▁then ▁began ▁to ▁arise ▁among ▁ordinary ▁people . ▁ ▁So cio - E conom ic ▁C aus es : ▁ ▁A part ▁from ▁political ▁causes , ▁labour ▁policies ▁were ▁also ▁implemented ▁to ▁sust ain ▁the ▁economy ▁of ▁the ▁region . ▁Lar ge ▁numbers ▁of ▁foreign ▁labour ers ▁were ▁brought ▁in ▁from ▁China ▁and ▁Java ▁to ▁meet ▁the ▁strong ▁demand ▁for ▁labour ▁in ▁ ▁East ▁Sum atra ' s ▁plant ation ▁economy ▁( which ▁made ▁up ▁ 6 4 ▁percent ▁of ▁economic ▁production ). ▁" In ▁the ▁case ▁of ▁the ▁plant ation ▁economy ▁in ▁this ▁region , ▁this ▁foreign ▁labour ▁was ▁pre domin antly ▁from ▁the ▁relatively ▁over c row ded ▁island ▁of ▁Java : ▁by ▁the ▁ 1 9 3 0 s , ▁ 4 3 ▁percent ▁of ▁the ▁population ▁was ▁' J avan ese ' ." ▁In ▁addition ▁to ▁the ▁Chinese ▁and ▁J avan ese ▁( who ▁number ed ▁about ▁ 1 9 2 , 0 0 0 ▁and ▁ 5 9 0 , 0 0 0 , ▁respectively ▁during ▁the ▁