1 9 3 0 s ), ▁the ▁economy ▁also ▁attract ed ▁migr ants ▁from ▁other ▁parts ▁of ▁the ▁Dutch ▁East ▁Ind ies . ▁As ▁a ▁result , ▁the ▁percent ages ▁of ▁the ▁three ▁main ▁ind igen ous ▁communities : ▁the ▁Malays , ▁Kar o ▁B ata ks ▁and ▁S imal ung un ▁B ata ks ▁in ▁the ▁region ▁were ▁significantly ▁reduced . ▁The ▁changes ▁in ▁social ▁structure ▁prompt ed ▁anx iety ▁among ▁the ▁people ▁of ▁East ▁Sum atra . ▁ ▁The ▁change ▁in ▁the ▁so cio - e conom ic ▁landscape ▁also ▁resulted ▁in ▁stark ▁class ▁differences ▁within ▁ ▁East ▁Sum at ran ▁society . ▁In ▁the ▁ 1 9 3 0 s , ▁many ▁far mers ▁of ▁the ▁to b acco ▁area ▁( D eli - Ser d ang - L ang k at ) ▁were ▁told ▁to ▁cultiv ate ▁smaller ▁areas ▁while ▁the ▁Mal ay ▁s ult ans , ▁S imal ung un ▁and ▁Kar o ▁ra jas ▁benef ited ▁from ▁prefer ential ▁treatment ▁by ▁the ▁Dutch ▁in ▁terms ▁of ▁land ▁le asing . ▁Those ▁arist ocr ats ▁were ▁able ▁to ▁accum ulate ▁significant ▁wealth ▁by ▁" le as [ ing ] ▁wide ▁tract s ▁of ▁land , ▁the ▁dispos al ▁rights ▁over ▁which ▁frequently ▁had ▁la in ▁tradition ally ▁with ▁the ▁village , ▁to ▁foreign ▁companies ..." ▁and ▁se izing ▁most ▁of ▁the ▁prof its . ▁Event ually , ▁most ▁of ▁the ▁rural ▁masses ▁went ▁to ▁seek ▁help ▁from ▁local ▁political ▁parties ▁such ▁as ▁G ER IN DO ▁( G