The were powerful territorial lords who ruled most of Japan from their vast, hereditary land holdings.
They were the most powerful feudal rulers from the 10th century to the early 19th century in Japan following the Shogun.
Though the term "daimyo" literally means "great name," the Japanese word actually comes from the kanji (characters) dai, meaning "large," and myō (shortened from myōden) meaning "name-land" or "private land."
From the shugo of the Muromachi period through the sengoku to the daimyo of the Edo period, the rank had a long and varied history.
The term "daimyo" is also sometimes used to refer to the leading figures of such clans, also called "lord". It was usually, though not exclusively, from these warlords that a shogun arose or a regent was chosen.
Major shugo daimyo came from the Shiba, Hatakeyama, and Hosokawa clans, as well as the tozama clans of Yamana, Ōuchi, and Akamatsu.The greatest ruled multiple provinces.
The Ashikaga shogunate required the shugo daimyo to reside in Kyoto, so they appointed relatives or retainers, called shugodai, to represent them in their home provinces. Eventually some of these in turn came to reside in Kyoto, appointing deputies in the provinces.
The Ōnin War was a major uprising in which shugo daimyo fought each other. During this and other wars of the time, kuni ikki, or provincial uprisings, took place as locally powerful warriors sought independence from the shugo daimyo. The deputies of the shugo daimyo, living in the provinces, seized the opportunity to strengthen their position. At the end of the fifteenth century, those shugo daimyo who succeeded remained in power. Those who had failed to exert control over their deputies fell from power and were replaced by a new class, the "sengoku daimyo," who arose from the ranks of the shugodai and Ji-samurai.
Around 1800, there were approximately 170 daimyo in Japan.
The shinpan were collaterals of Ieyasu, such as the Matsudaira, or descendants of Ieyasu other than in the main line of succession. Several shinpan, 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 rōjū. The fact that fudai daimyo could hold government positions while tozama, in general, could not was a main difference between the two.
Tozama daimyo held large 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 Chōshū, 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 kōtai, resulted in peaceful relations.
Upset by these controls, and often in bad economic situations because of things like sankin kotai, forced support of public works, and extravagant spending, several daimyo sided against the Tokugawa Shogunate during the Meiji Restoration.
In 1869, the year after the Meiji Restoration, the daimyo, together with the kuge, formed a new aristocracy, the kazoku. In 1871, the han were abolished and prefectures were established, thus effectively ending the daimyo era in Japan. In the wake of this change, many daimyo remained in control of their lands, being appointed as prefectural governors; however, they were soon relieved of this duty and called en masse to Tokyo, thereby cutting off any independent base of power from which to potentially rebel. Despite this, members of former daimyo families remained prominent in government and society, and in some cases continue to remain prominent to the present day.(For example, Morihiro Hosokawa, the former prime minister is a descendant of the daimyo of Kumamoto, but these cases are very few now.)