Ikkoku Heikinyaku (一国平均役)
Ikkoku heikinyaku refers to land taxes and assignments evenly imposed on shoen (manor) and kokugaryo (territories governed by a provincial government office) of a particular province during the Middle Ages in Japan. It is called ikkoku heikinyaku because taxes and assignments were imposed evenly (heikin) throughout a province.
Around the 9th or 10th century, the Ritsuryo system (a system of centralized government based on the ritsuryo code) and the Soyocho tax system collapsed and as a result, the taxes due changed into kanmotsu (tribute goods paid as taxes or tithes) and zatsueki (odd-job tasks). Meanwhile, the Imperial Court urgently needed to secure financial resources for incidental projects (construction, rituals, and so on). For this reason, in order to cover the expenses of such incidental events, from the late tenth century, a particular province was designated as a ryogoku and the kokushi (governor) of that ryogoku imposed temporary tasks mainly on the owners of koden (or kokugaryo - territories governed by a provincial government office). These temporary tasks included the provision of a service to build a palace, service daijoe (great thanksgiving), yakubukumai (rice tax levied by the grand shrine), building provincial monasteries, and building high-ranking shrines, and the provision of services or rice listed above was at the time called chokuji or inji kokuyaku (tasks or services imposed by the imperial court).
Temporary tasks and taxes were first collected from kokugaryo, but fuyu shoen that were exempt of tax submission expanded and as a result reduced kokugaryo, so the governor imposed taxes and tasks on fuyu shoen as well. In order to avoid paying taxes, owners of fuyu shoen influenced powerful aristocrats to obtain kanpu (official documents from Dajokan, or Great Council of State) or senji (an imperial letter) to become task or tax exempt; however, provincial governors then requested reinforcement of ikkoku heikin task or tax imposition to a superior authority, had their request approved, and countered fuyu shoen owners.
After these events, it is believed that the ikkoku heikinyaku system was officially established in the late 11th century, around the time of Emperor Gosanjo. Tax imposition in the ikkoku heikinyaku system was carried out based upon ota-bumi (cadastre created in the Kamakura period) created by kokuga (provincial government offices). Creation of ota-bumi is considered to be strongly related to ikkoku heikinyaku.
During the Jisho-Juei War at the end of the Heian period, the Taira administration levied military provisions from many provinces, and this was also considered as ikkoku heikinyaku. Also, to prepare for the Battle of Sunomatagawa, the Taira clan imposed zatsueki on Ise Province so they would provide sailors and ships, and in this case, a request for sailors and ships was issued within 10 days after a senji was issued to the provincial governor. This suggests that provinces had a system to immediately respond to the imposition of ikkoku heikinyaku taxes or tasks.
In the Kamakura period, there were many cases where shugo (provincial constable) seized power of kokuga instead of provincial governors, and as a result, the Kamakura bakufu (Japanese feudal government headed by a shogun) also started to impose ikkoku heikinyaku taxes and tasks. During the Muromachi period, ikkoku heikinyaku changed into tansen (a kind of provisional tax in medieval Japan).