▁and ▁to ▁peace ▁in ▁the ▁arch ip el ago . ▁The ▁increasing ▁number ▁of ▁Catholic ▁converts ▁in ▁southern ▁Japan ▁( main ly ▁Ky ū sh ū ) ▁was ▁a ▁significant ▁element ▁of ▁that ▁which ▁was ▁seen ▁as ▁a ▁threat . ▁Based ▁on ▁work ▁conducted ▁by ▁Japanese ▁histor ians ▁in ▁the ▁ 1 9 7 0 s , ▁some ▁sch ol ars ▁have ▁challeng ed ▁this ▁view , ▁bel ieving ▁it ▁to ▁be ▁only ▁a ▁partial ▁explanation ▁of ▁political ▁reality . ▁ ▁The ▁motiv ations ▁for ▁the ▁grad ual ▁strength ening ▁of ▁the ▁mar itime ▁prohib itions ▁during ▁the ▁early ▁ 1 7 th ▁century ▁should ▁be ▁considered ▁within ▁the ▁context ▁of ▁the ▁Tok ug awa ▁b ak uf u ' s ▁domestic ▁ag enda . ▁One ▁element ▁of ▁this ▁ag enda ▁was ▁to ▁ac quire ▁sufficient ▁control ▁over ▁Japan ' s ▁foreign ▁policy ▁so ▁as ▁not ▁only ▁to ▁guarantee ▁social ▁peace , ▁but ▁also ▁to ▁maintain ▁Tok ug awa ▁supre m acy ▁over ▁the ▁other ▁powerful ▁l ords ▁in ▁the ▁country , ▁particularly ▁the ▁to z ama ▁da im y ō s . ▁These ▁da im y ō s ▁had ▁used ▁East ▁Asian ▁trad ing ▁link ages ▁to ▁prof itable ▁effect ▁during ▁the ▁S eng oku ▁period , ▁which ▁allowed ▁them ▁to ▁build ▁up ▁their ▁military ▁strength ▁as ▁well . ▁By ▁restrict ing ▁the ▁da im y ō s ▁ability ▁to ▁trade ▁with ▁foreign ▁ships ▁coming ▁to ▁Japan ▁or ▁purs ue ▁trade ▁opportun ities ▁over se as , ▁the ▁Tok ug awa ▁b