The word origin was the expression "sengoku no yo (period of warring states)" by the court nobles at that time comparing the troubled social conditions since the Onin Disturbance to the troubled times in the "Chunqiu and Zhanguo periods (Spring and Autumn period and the Warring States period)" in ancient China.
応仁の乱以降の乱れた世相を、当時の公家が古代中国の「春秋戦国時代」の乱世になぞらえ「戦国の世」と表現したのが語源。