Osaka Castle: The Symbol of Japan’s Unification and the Rise of Toyotomi Hideyoshi

The man who brought an end to the Sengoku era and unified Japan — Toyotomi Hideyoshi (1536-1598; 豊臣秀吉). After his lord, Oda Nobunaga (1534-1582; 織田信長), was killed in the Honno-ji Incident by Akechi Mitsuhide, Hideyoshi moved with astonishing speed, defeating him and setting his sights on national domination.

Yet his rise was not built on military power alone.
Through masterful politics and strategy, he expanded his influence — and after Nobunaga’s death, maneuvered carefully to avoid being seen as a usurper. Instead, he established himself as the rightful successor to the Oda legacy. By reshaping these power dynamics to his advantage, he seized control and eventually confronted Nobunaga’s ally, Tokugawa Ieyasu (1542-1616, 徳川家康). With no decisive victory between them, Hideyoshi made a bold move: he became kampaku (Imperial Regent), rising above even the highest ranks of the samurai class.

The result was — Osaka Castle, the ultimate symbol of his power. Far more than a massive fortress, it was conceived as the center of a vast economic city — a strategic hub designed for ruling all of Japan.

Let us uncover the extraordinary intelligence and strategy that propelled Hideyoshi to the pinnacle of power.

Oda Nobunaga's Death

In the Medieval period (15th - 16th century), Toyotomi Hideyoshi began his service as a vassal to a rapidly growing military lord, Oda Nobunaga. Nobunaga defeated and subjugated his rival warlords one by one to end the Warring States Period with his military power, intelligence, and wealth. However, in 1582, the Honnoji incident occurred, and he was killed by his vassal, Akechi Mitsuhide, just before the unification of Japan. This brought an unexpected opportunity for Hideyoshi to become Nobunaga's successor.

The Positions of Katsuie and Hideyoshi are Reversed at the Kiyosu Conference

Following Nobunaga's death, a conference was held at Kiyosu Castle to determine the succession of Nobunaga and the redistribution of territory. At that time, there were three candidates to succeed Nobunaga: Nobunaga’s legitimate grandson, Hidenobu; his second son, Nobukatsu; and his third son, Nobutaka. Hideyoshi supported Hidenobu, who was only three years old, over Nobutaka, the candidate favored by Katsuie, a senior retainer of the Oda clan. Hidenobu was eventually selected as the head of the Oda family, granting Hideyoshi initial control over the family due to his ability to manipulate the young Hidenobu. In addition, Hideyoshi's territory was expanded, including the capital city of Kyoto, and reversed the power dynamic between Katsuie and Hideyoshi. In 1583, just nine months after the Kiyosu Conference, Hideyoshi defeated Katsuie at the Battle of Shizugatake. It is believed that Hideyoshi's ambition was not solely to succeed Nobunaga, but to achieve the same level of power and influence as Nobunaga as the ruler of the nation.

Osaka Castle, a Center of the Nation Ruled by Hideyoshi

In 1583, Hideyoshi began constructing Osaka Castle on the Uemachi Plateau. This location was strategically important as a transportation center for the logistical water network and was close to Kyoto, where the emperor resided, along the Yodo River. It was also connected to the western region by the Seto Inland Sea, where there were still warlords who were not under Hideyoshi's control. The central castle tower was completed in 1585, and it was said to be a symbol of Hideyoshi's power, with its large five-story keep adorned with gold leaf tiles and golden orcas on the roof. It had a huge reception hall with 1,000 tatami mats inside.
The castle also provided an impregnable defense surrounding the entire castle town with a moat, stone walls, and natural rivers. The castle town was built on the west side of Osaka Castle, facing Osaka Bay, and four major canals were constructed to provide a distribution network for water transportation. The streets were laid out in an orderly grid pattern, and roads were constructed. At the same time, an epoch-making urban development was achieved with the creation of sewers. Hideyoshi also created shipping docks and invited merchants to come to Osaka, thereby revitalizing the city's economy. As a man of the nation, Hideyoshi built a political and economic center on the Uemachi Plateau, accomplishing what his lord Nobunaga had failed to do. This plateau was the site that Nobunaga had been eager to seize, even if it took a decade-long battle against the Osaka Honganji Temple.

Hideyoshi Rose to Becomes the Ruler of Japan

Through skillful tactics and negotiations, Hideyoshi began his path to becoming the ruler of Japan. He carefully subdued or persuaded Nobunaga's retainers, brothers, and sons. Though he could defeat them by force, that would mirror Mitsuhide's betrayal, so he advanced gradually and steadily, ultimately reversing the master-servant relationship with the Oda family.

At the same time, he continued with the construction of Osaka Castle and its town. Standing in his way was Nobunaga's partner, Tokugawa Ieyasu. The following year, after the construction of Osaka Castle began, they battled at Komaki and Nagakute. However, the fight ended inconclusively, and they agreed to peace. In 1585, Hideyoshi became the first-ever kanpaku (a chief advisor to the emperor), remaining a samurai, rather than becoming shogun. This made him supreme over the Oda family, Ieyasu, and all the samurai.

In 1590, Hideyoshi besieged Odawara Castle—the stronghold of the Hojo clan, rulers of the Kanto region—with an army of 200,000 troops, forcing its surrender. The following year, in 1591, he dispatched another force of 60,000 soldiers to the Oshu region (northeastern Japan) to subdue the area. With these campaigns, he succeeded in unifying the country.

The End of Hideyoshi

In March 1598, after holding a cherry blossom viewing party at Daigoji Temple, Hideyoshi's health began to deteriorate. By May, his condition had worsened, and he passed away on August 18 at the age of 61. His farewell poem reads:

I was born in this world like a dewdrop, and now I am disappearing like a dewdrop.
Even though I am a man of the world, what I have created in Osaka is nothing but a fleeting dream within a dream.
(露と落ち　露と消えにし我が身かな　浪速のことは　夢のまた夢)

Hideyoshi was an unparalleled samurai who rose from humble beginnings as a farmer to become a great unifier of Japan.

Toyotomi Hideyoshi Timeline

1537	Hideyoshi was born in Nagoya	Age=1	Azuchi Momoyama Period
1554	Hideyoshi started to work under Nobunaga	16
1582	Shibata Katsuie fought against Uesugi clan in Echu Province	45
1582	Nobunaga was killed at Honnoji by Akechi Mitsuhide	45
1582	Hideyoshi defeated Akechi Mitsuhide	45
1582	The Kiyosu Conference was held	45
1583	Hideyoshi defeated Sibata Katsuie	46
1583	Hideyoshi started to build Osaka castle	49
1584	The battle of Komaki Nagakute between Hideyoshi and Ieyasu	50
1585	Hideyoshi was appointed to Kanpaku	51
1590	Hideyoshi unified the nation	53
1598	Hideyoshi enjoyed the cherry blossom viewing at Daigoji Temple	61
1598	Hideyoshi passed away	61
1603	Ieyasu estabished Tokugawa shogunate at Edo	-	Edo
1614	The Winter Siege of Osaka	-
1615	The Summer Siege of Osaka and Toyotomi clan fell	-

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