Watakushiikusa (also called shisen [private warfare]) is a small-scale military/battle conducted in Japan before the early-modern period for Katakiuchi (revenge) or for self-preservation, without an official order such as Daijokanpu (official documents of Daijokan, which is the office of the supreme political leader), senji (imperial decree) or an order from bakufu (Japanese feudal government headed by a shogun).
私軍（わたくしいくさ・私戦（しせん））とは、近世以前の日本において太政官符や宣旨、幕府の命令などの公的命令によらずして、敵討や自力救済のために行われる小規模な武力行使・戦闘行為。