Sengoku period

During this period, although the Emperor of Japan was officially the ruler of his nation and every lord swore loyalty to him, he was largely a marginalized, ceremonial, and religious figure who delegated power to the shōgun, a noble who was roughly equivalent to a general. In the years preceding this era, the shogunate gradually lost influence and control over the daimyōs (local lords). Although the Ashikaga shogunate had retained the structure of the Kamakura shogunate and instituted a warrior government based on the same socio-economic rights and obligations established by the Hōjō with the Jōei Code in 1232, it failed to win the loyalty of many daimyō, especially those whose domains were far from the capital, Kyoto. Many of these lords began to fight with each other for control over land and influence over the shogunate. As trade with Ming China grew, the economy developed, and the use of money became widespread as markets and commercial cities appeared. Combined with developments in agriculture and small-scale trading, this led to the desire for greater local autonomy throughout all levels of the social hierarchy. As early as the beginning of the 15th century, the suffering caused by earthquakes and famines often served to trigger armed uprisings by farmers weary of debt and taxes.

Historians most often consider the Ōnin War (1467–1477), a ten-year conflict wrought by political turmoil, to be the trigger for what would come to be known as the Sengoku period. This civil war would clearly exemplify the Ashikaga Shogunate’s waned authority over its shogunal administration, the provincial daimyo and Japan as a whole; thereby a wave of unbridled conflict would spread across Japan and consume the states in an age of war. It is suggested by both scholars and authors that “these succession disputes still might not have led to war were it not for the shōgun’s lack of leadership.”[6][7]

The Ōnin War, which devastated two-thirds of Kyoto, was an event that rippled disarray across Japan.[6] In addition to the military confrontations between separate states, there was also domestic fallout. In contempt of the shogunate, the daimyo who were subjected to remain in Kyoto instead returned to their provinces. Consequentially, some of these daimyo found that their designated retainers or shugodai, representatives of their states appointed in a daimyo’s absence, rose in power either to seize control of the domain or proclaim independence as a separate domain.[7]

Furthermore, weariness of war, socioeconomic unrest and poor aristocratical treatment invoked the wrath of the peasant class. Farmers, craftsmen, merchants and even villages would organize uprisings (known as “ikki”) against the ruling class. An extraordinary example of this can be observed in the Kaga Rebellion, in which the local ikki had staged a large-scale revolt with the support of the True Pure Land sect (thereby establishing the term ikkō ikki) and assumed control of the entire province of Kaga.[7][8]

The period culminated with a series of three warlords – Oda Nobunaga, Toyotomi Hideyoshi, and Tokugawa Ieyasu – who gradually unified Japan. After Tokugawa Ieyasu's final victory at the siege of Osaka in 1615, Japan settled down into over 200 years of peace under the Tokugawa shogunate.

The Ōnin War in 1467 is usually considered the starting point of the Sengoku period. There are several events which could be considered the end of it: Nobunaga's entry to Kyoto (1568)[9] or abolition of the Muromachi shogunate (1573)[10] or entry into Azuchi Castle (1576), Hideyoshi's promulgation of the Sōbujirei (ja) law prohibiting war (1587), the siege of Odawara (1590), the Battle of Sekigahara (1600), the establishment of the Tokugawa shogunate (1603), the siege of Osaka (1615), or the suppression of the Shimabara Rebellion (1638).[1][2]

Japan in 1570

The upheaval resulted in the further weakening of central authority, and throughout Japan, regional lords, called daimyōs, rose to fill the vacuum. In the course of this power shift, well-established clans such as the Takeda and the Imagawa, who had ruled under the authority of both the Kamakura and Muromachi bakufu, were able to expand their spheres of influence. There were many, however, whose positions eroded and were eventually usurped by more capable underlings. This phenomenon of social meritocracy, in which capable subordinates rejected the status quo and forcefully overthrew an emancipated aristocracy, became known as gekokujō (下克上), which means "low conquers high".[11]

One of the earliest instances of this was Hōjō Sōun, who rose from relatively humble origins and eventually seized power in Izu Province in 1493. Building on the accomplishments of Sōun, the Hōjō clan remained a major power in the Kantō region until its subjugation by Toyotomi Hideyoshi late in the Sengoku period. Other notable examples include the supplanting of the Hosokawa clan by the Miyoshi, the Toki by the Saitō, and the Shiba clan by the Oda clan, which was in turn replaced by its underling, Toyotomi Hideyoshi, a son of a peasant with no family name.

Well-organized religious groups also gained political power at this time by uniting farmers in resistance and rebellion against the rule of the daimyōs. The monks of the Buddhist True Pure Land sect formed numerous Ikkō-ikki, the most successful of which, in Kaga Province, remained independent for nearly 100 years.

Japan in the late 16th century

After nearly a century of political instability and warfare, Japan was on the verge of unification by Oda Nobunaga, who had emerged from obscurity in the province of Owari (present-day Aichi Prefecture) to dominate central Japan. In 1582, while in Kyoto at the temple of Honnō-ji, Oda Nobunaga committed seppuku during an invasion of the temple led by one of his generals, Akechi Mitsuhide, in order to assassinate Oda. This allowed Toyotomi Hideyoshi the opportunity to establish himself as Oda's successor after rising through the ranks from ashigaru (footsoldier) to become one of Oda's most trusted generals. Toyotomi eventually consolidated his control over the remaining daimyōs but ruled as Kampaku (Imperial Regent) as his common birth excluded him from the title of Sei-i Taishōgun. During his short reign as Kampaku, Toyotomi attempted two invasions of Korea. The first attempt, spanning from 1592 to 1596, was initially successful but suffered setbacks from the Joseon Navy and ended in a stalemate. The second attempt began in 1597 but was less successful as the Koreans, especially their navy, led by Admiral Yi Sun-Sin, were prepared from their first encounter. In 1598, Toyotomi called for retreat from Korea prior to his death.

Ōzutsu (Big Gun)

Without leaving a capable successor, the country was once again thrust into political turmoil, and Tokugawa Ieyasu took advantage of the opportunity.[12]

On his deathbed, Toyotomi appointed a group of the most powerful lords in Japan—Tokugawa, Maeda Toshiie, Ukita Hideie, Uesugi Kagekatsu, and Mōri Terumoto—to govern as the Council of Five Regents until his infant son, Hideyori, came of age. An uneasy peace lasted until the death of Maeda in 1599. Thereafter a number of high-ranking figures, notably Ishida Mitsunari, accused Tokugawa of disloyalty to the Toyotomi regime.

This precipitated a crisis that led to the Battle of Sekigahara in 1600, during which Tokugawa and his allies, defeated the anti-Tokugawa forces. Generally regarded as the last major conflict of the Sengoku period, Tokugawa's victory at Sekigahara made him the leading foce inside the Toyotomi regime, the last remnants of which were finally destroyed in the siege of Osaka in 1615.

• List of daimyōs from the Sengoku period
• List of Japanese battles
• Horses in East Asian warfare
• Warring States period – a similar period in Chinese history
• Crisis of the Third Century – a similar period in Roman history
• Kabukimono

• Warring-States Japan Battle Dataset – 2,889 battles occurring within Japan during the Sengoku period
• Sengoku Period - World History Encyclopedia
• Samurai Archives Japanese History page
• (in Japanese) Sengoku Expo: Japanese Design, Culture in the Age of Civil Wars held in Gifu Prefecture, 2000–2001
• (in Japanese) List of the Sengoku Daimyos