The Sengoku Period and Sekigahara: From the Onin War to the Siege of Osaka, and Himeji Castle, Osaka Castle, and the Sekigahara Battlefield Today

The Sengoku, or Warring States, period usually runs from the Onin War of 1467 to the fall of the Toyotomi family in the Summer Siege of Osaka in 1615, about 150 years. Regional lords fought one another until three men, Oda Nobunaga, Toyotomi Hideyoshi, and Tokugawa Ieyasu, unified the country in turn. Most of the castles, warlords, and battles that Japanese people know best come from this period. The sections below follow it in order and match it to castles and battlefields you can visit.

The Onin War: eleven years of fighting in Kyoto

The Warring States period began in Kyoto. In 1467 a succession dispute in the Muromachi shogun’s family became tangled with rivalries between powerful provincial governors, and Eastern and Western armies started fighting in the capital. This was the Onin War, which lasted until 1477. Large parts of Kyoto burned, and many temple and shrine buildings there were rebuilt after it.

By the time it ended, the Muromachi shogunate could no longer control the provinces. Warlords who seized land by force, the sengoku daimyo, appeared everywhere, and retainers overthrowing their lords or local strongmen replacing governors became common, a trend called gekokujo, “the low overturning the high”.

Firearms and a new kind of castle

Amid the wars between lords, two things changed how fighting worked. One was the matchlock gun, brought in 1543 by Portuguese who washed up on Tanegashima, in today’s Kagoshima, and soon copied in large numbers at Sakai and Kunitomo. The other was the castle. Defensive hilltop forts gave way to castles on low hills or flat ground that also served as seats of government, with a tall central keep, the tenshu.

Only 12 castles in Japan still have keeps built before the Edo period ended, known as the 12 original keeps. The most famous, Himeji Castle in Hyogo, had its keep completed by Ikeda Terumasa in 1609, and in 1993 it became one of Japan’s first World Heritage sites, together with Horyu-ji in Nara. Since March 1, 2026, admission is JPY 2,500 for visitors aged 18 and over who live outside Himeji, JPY 1,000 for Himeji residents, and free for under-18s. The castle is open from 9:00 to 17:00, with last entry at 16:00.

Sources: Himeji Castle official site, Kobe Shimbun: Himeji Castle’s two-tier pricing (March 2026).

From Nobunaga to Hideyoshi: the first half of unification

The warlord best known for using guns was Oda Nobunaga. In 1560 he defeated the far larger army of Imagawa Yoshimoto at Okehazama, and in 1573 he drove the shogun Ashikaga Yoshiaki out of Kyoto, ending the Muromachi shogunate. At the Battle of Nagashino in 1575 he used massed guns to beat the Takeda army, and from 1576 he built Azuchi Castle, with a lavish keep, on the shore of Lake Biwa. In 1582 his retainer Akechi Mitsuhide attacked him at Honno-ji temple in Kyoto, and Nobunaga took his own life. This is the Honno-ji Incident.

Toyotomi Hideyoshi took over. He quickly defeated Mitsuhide and in 1583 began building Osaka Castle on the site of the Ishiyama Hongan-ji temple. In 1588 his sword hunt took weapons away from farmers, he carried out a nationwide land survey, and in 1590 he took Odawara from the Hojo clan, completing the unification of Japan. In 1592 and 1597 he sent armies to the Korean Peninsula (the Bunroku and Keicho campaigns), causing severe destruction in Korea, before the troops withdrew after his death in 1598.

Today’s Osaka Castle keep is a reinforced-concrete rebuild paid for by Osaka citizens’ donations in 1931, and inside is a museum on the castle’s history. Adult admission is JPY 1,200. Hideyoshi’s castle burned in 1615, and most of the stone walls you see now were built when the Tokugawa shogunate rebuilt it.

Source: Osaka Castle Main Tower.

Sekigahara: the country decided in a day

After Hideyoshi’s death, Tokugawa Ieyasu, who held real power, clashed with Ishida Mitsunari, who sought to protect the Toyotomi regime. On Keicho 5, 9th month, 15th day (October 21, 1600), Ieyasu’s Eastern Army and Mitsunari’s Western Army met at Sekigahara in Mino Province, today’s Sekigahara, Gifu. In the Battle of Sekigahara, the Western commander Kobayakawa Hideaki switched sides mid-battle, and the outcome was settled in about a day.

Ieyasu was appointed shogun in 1603 and opened his shogunate in Edo. The Toyotomi family held on in Osaka Castle, but fell after the Winter Siege of 1614 and the Summer Siege of 1615, and Japan entered a long peace. The era name changed to Genna that year, so the peace that followed is called Genna Enbu.

Markers for each commander’s position are scattered across the Sekigahara battlefield. The Gifu Sekigahara Battlefield Memorial Museum, opened in 2020, recreates the battle with film and displays, and its fifth-floor observation room looks out over the whole field. Adult admission is JPY 500, from 9:30 to 17:00, closed on Mondays. It is about a 10-minute walk from JR Sekigahara Station.

Source: Gifu Sekigahara Battlefield Memorial Museum.

Common misunderstandings

Last, a few points that are often confused.

The first is thinking Sekigahara ended the Warring States period. It decided who held power, but the Toyotomi family fell only in the Summer Siege of Osaka in 1615, and the fighting truly ended after that.

The second is taking Osaka Castle’s keep for a Toyotomi-era building. The current keep is a 1931 reinforced-concrete rebuild, and much of the stonework dates from the Tokugawa era. To see an original pre-modern keep, go to Himeji, Matsumoto, Hikone, or another of the original-keep castles.

The third is looking for the site of the incident at today’s Honno-ji. After the incident Hideyoshi moved the temple to its present spot near Teramachi-Oike, and the original site, in the Motohonnojicho area to the west, is marked only by a stone.

The fourth is calling everything up to 1603 the Sengoku period. Historians end it variously in 1573, 1590, or 1615, and the years of Nobunaga and Hideyoshi, 1573 to 1603, are often called the Azuchi-Momoyama period instead.

Useful terms

• Onin no Ran: the Onin War
• Gekokujo: the low overturning the high
• Honno-ji no Hen: the Honno-ji Incident
• Sekigahara no Tatakai: the Battle of Sekigahara
• Genzon tenshu: original surviving castle keeps

References

• Himeji Castle official site
• Kobe Shimbun: Himeji Castle’s two-tier pricing (March 2026)
• Osaka Castle Main Tower
• Gifu Sekigahara Battlefield Memorial Museum