▁the ▁University ▁of ▁Chicago ▁before ▁accepting ▁an ▁appointment ▁as ▁professor ▁of ▁history ▁at ▁Harvard ▁University ▁in ▁ 1 9 8 9 , ▁where ▁he ▁became ▁Charles ▁Warren ▁Professor ▁of ▁American ▁History ▁in ▁ 1 9 9 1 . ▁He ▁was ▁director ▁of ▁the ▁Ed win ▁O . ▁Re isch auer ▁Institute ▁of ▁Japanese ▁Studies ▁from ▁ 1 9 9 1 ▁through ▁ 1 9 9 5 . ▁ ▁Since ▁ret iring ▁in ▁ 2 0 0 5 , ▁he ▁has ▁taught ▁at ▁W ased a ▁University , ▁R its ume ikan ▁University , ▁and ▁the ▁University ▁of ▁Illinois ▁as ▁a ▁guest ▁professor . ▁ ▁Career ▁and ▁scholar ship ▁The ▁focus ▁of ▁his ▁research ▁and ▁thinking ▁first ▁turned ▁to ▁the ▁United ▁States , ▁China , ▁and ▁Japan ' s ▁interactions ▁in ▁the ▁period ▁leading ▁up ▁to ▁the ▁Pacific ▁War , ▁a ▁war ▁which ▁he ▁experienced ▁first ▁hand ▁as ▁a ▁child . ▁His ▁first ▁book , ▁After ▁Imperial ism : ▁The ▁Search ▁for ▁a ▁New ▁Order ▁in ▁the ▁Far ▁East , ▁ 1 9 2 1 – 1 9 3 1 , ▁based ▁on ▁his ▁Ph D ▁th esis , ▁made ▁use ▁of ▁the ▁multi - arch ival ▁and ▁multi - ling ual ▁research ▁which ▁character izes ▁his ▁scholar ship . ▁The ▁book ▁presents ▁the ▁argument ▁that ▁the ▁collapse ▁of ▁the ▁" di plom acy ▁of ▁imperial ism " ▁after ▁Tre aty ▁of ▁Vers a illes ▁left ▁a ▁vac u um ▁in ▁the ▁East ▁Asian ▁international ▁system , ▁a ▁theme ▁also ▁expl ored ▁in ▁his