The daimyo (大名: daimyō) were the most powerful feudal rulers from the 12th century to the 19th century in Japan. The term daimyo literally means "great name". From the shugo daimyo of the Kamakura period through the sengoku daimyo to the daimyo of the Edo period, the rank had a long and varied history. In 1869, the year after the Meiji restoration, the daimyo together with the kuge formed a new aristocratic group, the kazoku, bringing an end to the daimyo.
Similar to the feudal system in Europe, they held dynastic control over territories that had varying degrees of autonomy; lesser territorial lords were pledged to support greater ones. A warrior-caste of samurai soldiers likewise gave their personal loyalty to the support of lords from these families.
At the beginning of the Edo period, their clans and territories were reorganized into the han, based on their production of rice. Daimyo headed han assessed at 10 000 koku (50 000 bushels) or more.
Especially at the beginning of the Edo period, they fell into three main groups: tozama daimyo (who as a result of the Battle of Sekigahara had agreed to submit to the rule of Tokugawa Ieyasu), fudai daimyo (who prior to that time had already been vassals of the Tokugawa), and shinpan (who were related to the Tokugawa).
The tozama daimyo held larger fiefs, with the Kaga han of Ishikawa Prefecture, headed by the Maeda clan, assessed at 1 000 000 koku. Other famous tozama clans included the Mori of Choshu, the Shimazu of Satsuma, the Date of Sendai, the Uesugi of Yonezawa, and the Hachisuka of Awa. Initially, the Tokugawa regarded them as potentially rebellious, but for most of the Edo period, marriages between the Tokugawa and the tozama, as well as control policies such as sankin kotai, resulted in peaceful relations.
The shimpan were collaterals of Ieyasu, such as the Matsudaira, or descendants of Ieyasu other than in the main line of succession. Several shimpan, including the Tokugawa of Owari (Nagoya), Kii (Wakayama) and Mito, as well as the Matsudaira of Fukui and Aizu, held large han.
A few fudai daimyo, such as the Ii of Hikone, held large han, but many were small. The shogunate placed many fudai at strategic locations to guard the trade routes and the approaches to Edo. Also, many fudai daimyo took positions in the Edo shogunate, some rising to the position of roju.
During the Edo period, the Tokugawa forced all daimyo to spend every other year in Edo, leaving family members behind in their han. This increased political and fiscal control over the daimyo by Edo. The term for this is sankin kōtai.
The term daimyo is also sometimes used to refer to the leading figures of such clans, also called "warlords". It was usually, though not exclusively, from these warlords that a shogun arose or a regent was chosen.