The present paper attempts to clarify the basic movements of the Oyama Family (小山氏) of Shimotsuke province (下野国), a warrior clan who, together, with the Ashikaga Family, played a central role as one of the "patrician" families of the eastern provinces during the Muromachi and Sengoku periods. The method of analysis utilized takes on the form of individual investigations concerning consecutive Oyama family heads. As a result of organizing both documents issued and received by these family leaders on the basis of a complete analysis of such objective data, a preinitiation name (osanana 幼名), current name (tsusho 通称), given name conferred at initiation (namae 名前), title in the central goverment (kanto 官途), title in the provinces (juryo 受領), and abbreviated signature (kakiHan 花押), the author attempts to shed light on the fundamental political and historical substance of the generational changes which took place during the resurgence of the clan following the rebellion of Oyama Yoshimasa (小山義政) in the Namboku-cho period. The study begins with Yasutomo (泰朝) and continues through the family headships from Mitsuyasu (満泰), to Mochimasa (持政), Shigenaga (成長), Masanaga (政長), Takatomo (高朝), Hidetsuna (秀綱), Masatane (政種), and Hidemune (秀宗). The investigation demonstrates that not only the objective documentary evidence was born from a regular pattern of change, but also the particular generational changes were in many cases marked by intra-family conflicts. Also, within this historical process the author sees an important function played by the relationship of the Oyama Family to the Muromachi Bakufu government in the eastern provinces (Koga Kubo 古河公方). The conclusion that it was this close relationship to the Koga Kubo Ashikaga Family which determined the political destiny of the resurrected Oyama Family during the Muromachi and Sengoku periods. That is, the decline of the eastern Ashikaga Family power in the late Sengoku period necessarily led to the fall of the Oyama clan and consequently paved the way for its later retainership ties to the Go-Hojo Family (後北条氏).

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