Mr. Oyama

A powerful clan in Shimotsuke in the Middle Ages. Its founder was Masamitsu, son of Ota Yukimasa, the 9th-generation grandson of Fujiwara no Hidesato. Masamitsu entered Shimotsuke as Shimotsuke Daijo during the Hogen and Heiji eras, and based in Oyamasho, Tsuga County (Samukawa Mikuriya, Oyama City, Tochigi Prefecture), he gained real power in administrative investigations at the provincial government office and expanded his influence. Masamitsu's eldest son, Tomomasa, succeeded the Oyama clan, while his second son, Munemasa, became the ancestor of the Naganuma clan, and his third son, Tomomitsu, became the ancestor of the Yuki clan. The Oyama clan was a powerful vassal of the Kamakura Shogunate during its early days, and held the position of Shugo of Shimotsuke throughout the Kamakura and Nanboku-cho periods. They also held the position of Shugo of Harima for a time, and a branch of the clan, the Naganuma clan, was appointed Shugo of Awaji. Their territories and positions included the Gon-no-Osukeshiki (provisional vassal position), the vast Kokugaryo (provincial government territory) area centered on the Kokufu (provincial capital), and the Jito (local steward) positions scattered throughout the country.

Hidetomo sided with Ashikaga Tadayoshi during the Nakasendai Rebellion in July 1335 (Kenmu 2) and was killed in battle. His successor, Tomosato (originally Tomou-ji), was ordered by Emperor Godaigo in August of the same year to handle national affairs in Resignation. In 1341 (Kokoku 2, Ryakuo 4), he organized the Toshi Ikki, a Fujiwara alliance, and the former regent Konoe Tsunetada took power throughout the country. He himself became the Bando Kanrei and dreamed of establishing a "Third Dynasty" that was neither the Southern nor the Northern Court. He took unique actions and became renowned as the foremost military commander in northern Kanto. In 1380 (Tenju 6, Koryaku 2), Yoshimasa came into conflict with Utsunomiya Mototsuna over control of the peasants, and was defeated by Kamakura kubo Ashikaga Ujimitsu, resulting in the demise of the Oyama clan. Ujimitsu was reluctant to see the demise of his noble family, so he had his relative Yuki Motomitsu's second son Yasutomo revive the Oyama clan. This is how the Oyama clan was reborn. Eventually, at the end of the Sengoku period, Hidetsuna joined the Hojo clan, and in 1590 (Tensho 18), Toyotomi Hideyoshi confiscated his territory, leading to the downfall of the Oyama clan.

[Takashi Shinkawa]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

中世の下野(しもつけ)の豪族。始祖は藤原秀郷(ふじわらのひでさと)9世の孫大田行政(ゆきまさ)の子政光(まさみつ)。政光は保元(ほうげん)・平治(へいじ)のころ、下野大掾(だいじょう)として下野に入部し、都賀(つが)郡小山荘＝寒河御厨(さむかわみくりや)（栃木県小山市域）を拠点に、国衙(こくが)の行政検断などの実権を握り勢力を拡大した。政光の長子朝政(ともまさ)は小山氏を継ぎ、また次男宗政(むねまさ)は長沼(ながぬま)氏、三男朝光(ともみつ)は結城(ゆうき)氏の祖となった。小山氏は、鎌倉幕府創業期の有力御家人(ごけにん)として重きをなし、鎌倉～南北朝時代を通じて下野の守護職を相承した。また一時期播磨(はりま)の守護職も兼ね、支族長沼氏は淡路の守護に任じた。その所領・所職(しょしき)は、権大介職(ごんのおおすけしき)および国府を中心とする広大な国衙領の郷々や、全国に散在する地頭職である。

　秀朝(ひでとも)は1335年（建武2）7月の中先代(なかせんだい)の乱に際して足利直義(あしかがただよし)方に味方し戦死、その後を継いだ朝郷(ともさと)（初め朝氏(ともうじ)）は同年8月、後醍醐(ごだいご)天皇から下野の国務を命ぜられ、また1341年（興国2・暦応4）藤原同盟である藤氏一揆(とうしいっき)を組織して、前関白近衛経忠(このえつねただ)が天下の政権をとり、自らは坂東管領(ばんどうかんれい)となって南朝でも北朝でもない「第三王朝」の建設を夢みるなど独自な行動をとり、北関東随一の武将として名をはせた。1380年（天授6・康暦2）義政(よしまさ)は、百姓支配をめぐり宇都宮基綱(うつのみやもとつな)と対立し、鎌倉公方(くぼう)足利氏満(うじみつ)の討伐を受け、小山氏は滅亡した。氏満は名家の断絶を惜しみ、同族の結城基光(もとみつ)の次男泰朝(やすとも)をして小山家を再興せしめた。これが重興小山氏である。やがて戦国時代末、秀綱(ひでつな)は北条氏に属したため、1590年（天正18）豊臣秀吉(とよとみひでよし)に所領を没収され滅亡した。

［新川武紀］

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