▁massive ▁civil ▁wars ▁in ▁the ▁south ▁and ▁the ▁rise ▁of ▁regional ▁war l ords ▁in ▁the ▁War l ord ▁Era . ▁Con sequently , ▁Out er ▁Mong olia ▁sought ▁Russian ▁support ▁to ▁claim ▁its ▁independence . ▁In ▁ 1 9 1 9 , ▁Chinese ▁general ▁X u ▁Sh uz h eng ▁advanced ▁into ▁Out er ▁Mong olia ▁and ▁ann ul led ▁its ▁independence . ▁In ▁ 1 9 2 1 , ▁Chinese ▁forces ▁were ▁driven ▁out ▁by ▁White ▁Russian ▁forces ▁led ▁by ▁Baron ▁Roman ▁von ▁Ung ern - S tern berg . ▁Some ▁months ▁later ▁they ▁were ▁driven ▁out ▁by ▁the ▁Red ▁Army ▁of ▁the ▁Russian ▁Soviet ▁Feder ative ▁Social ist ▁Republic , ▁the ▁Far ▁Eastern ▁Republic ▁and ▁pro - S ov iet ▁Mong ol ian ▁forces . ▁In ▁ 1 9 2 4 , ▁the ▁Mong ol ian ▁People ' s ▁Republic ▁was ▁proc laimed . ▁With ▁the ▁on set ▁of ▁the ▁Japanese ▁invasion ▁of ▁China , ▁little ▁effort ▁was ▁given ▁to ▁re est ab lish ▁Chinese ▁control ▁over ▁Out er ▁Mong olia . ▁ ▁Following ▁the ▁end ▁of ▁World ▁War ▁II , ▁the ▁Republic ▁of ▁China , ▁led ▁by ▁the ▁Ku om int ang , ▁was ▁forced ▁to ▁formally ▁accept ▁Out er ▁Mong ol ian ▁independence ▁under ▁Soviet ▁pressure . ▁In ▁ 1 9 4 9 , ▁the ▁Commun ists ▁won ▁the ▁Chinese ▁Civil ▁War ▁and ▁re - recogn ized ▁Mong olia ' s ▁independent ▁status . ▁ ▁Commun ist ▁era ▁ ▁The ▁People ' s ▁Republic ▁of ▁China ▁ ▁established