After Genko (Mongol invasion attempt against Japan), a movement to exchange ichienchi (land under ichien shihai) in Kyushu owned by the lords of shoen and those in the western part of Japan owned by jito became active because of the need to defend the coast.
更に元寇以降、海岸防備の必要性から九州を中心とする領主側の一円地と、西国の地頭側一円地を交換する動きが活発化した。