▁police ▁of ▁Nag as aki ▁could ▁har ass ▁them ▁at ▁will , ▁and ▁at ▁all ▁times ▁a ▁strong ▁Japanese ▁guard ▁was ▁station ed ▁on ▁the ▁narrow ▁bridge ▁to ▁the ▁main land ▁in ▁order ▁to ▁prevent ▁them ▁from ▁leaving ▁the ▁island . ▁ ▁Term in ology ▁ ▁Trade ▁in ▁fact ▁prosper ed ▁during ▁this ▁period , ▁and ▁though ▁relations ▁and ▁trade ▁were ▁restricted ▁to ▁certain ▁ports , ▁the ▁country ▁was ▁far ▁from ▁closed . ▁In ▁fact , ▁even ▁as ▁the ▁sh og un ate ▁exp elled ▁the ▁Portuguese , ▁they ▁simultaneously ▁engaged ▁in ▁discuss ions ▁with ▁Dutch ▁and ▁Korean ▁represent atives ▁to ▁ensure ▁that ▁the ▁overall ▁volume ▁of ▁trade ▁did ▁not ▁suffer . ▁Thus , ▁it ▁has ▁become ▁increasing ly ▁common ▁in ▁scholar ship ▁in ▁recent ▁dec ades ▁to ▁refer ▁to ▁the ▁foreign ▁relations ▁policy ▁of ▁the ▁period ▁not ▁as ▁s ak oku , ▁imp lying ▁a ▁totally ▁se cluded , ▁isolated , ▁and ▁" closed " ▁country , ▁but ▁by ▁the ▁term ▁ka ik in ▁( 海 <0xE7> <0xA6> <0x81> , ▁" mar itime ▁prohib itions ") ▁used ▁in ▁documents ▁at ▁the ▁time , ▁and ▁derived ▁from ▁the ▁similar ▁Chinese ▁concept ▁ha ij in . ▁ ▁R ationale ▁▁ ▁It ▁is ▁convention ally ▁regarded ▁that ▁the ▁sh og un ate ▁im posed ▁and ▁enfor ced ▁the ▁s ak oku ▁policy ▁in ▁order ▁to ▁remove ▁the ▁colonial ▁and ▁religious ▁influence ▁of ▁primarily ▁Spain ▁and ▁Portugal , ▁which ▁were ▁perce ived ▁as ▁pos ing ▁a ▁threat ▁to ▁the ▁stability ▁of ▁the ▁sh og un ate