Tokugawa Ieyasu

As Oda Nobuhide continued to attack Okazaki, Hirotada turned to his powerful eastern neighbor, Imagawa Yoshimoto for assistance. Yoshimoto agreed to an alliance under the condition that Hirotada send his young heir to Sunpu Domain as a hostage.[5] Oda Nobuhide learned of this arrangement and had Takechiyo abducted.[7] Takechiyo was five years old at the time.[8] Nobuhide threatened to execute Takechiyo unless his father severed all ties with the Imagawa clan. However, Hirotada refused, stating that sacrificing his own son would show his seriousness in his pact with the Imagawa. Despite this refusal, Nobuhide chose not to kill Takechiyo, but instead held him hostage for the next three years at the Honshōji Temple in Nagoya. It is said that Oda Nobunaga met Takechiyo at this place, when Takechiyo was 6 years old, and Nobunaga was 14 at that time.

In 1549, when Takechiyo was 6,[8] his father Hirotada was murdered by his own vassals, who had been bribed by the Oda clan. At about the same time, Oda Nobuhide died during an epidemic. Nobuhide's death dealt a heavy blow to the Oda clan.

In 1551, an army under the command of Imagawa Sessai laid siege to the castle where Oda Nobuhiro, Nobuhide's illegitimate eldest son was living. Nobuhiro was trapped by the Imagawa clan but was saved by Oda Nobunaga, Nobuhide's second son and heir, through negotiations. Sessai made an agreement with Nobunaga to take Takechiyo back to Imagawa, and he agreed. So Takechiyo (now nine years old) was taken as a hostage to Sunpu. At Sunpu, he remained a hostage but was treated fairly well as a potentially useful future ally of the Imagawa clan until 1556 when he was 14 years old.[8]

By 1559 the leadership of the Oda clan had passed to Oda Nobunaga. In 1560, Imagawa Yoshimoto leading a large army of 25,000 men, invaded Oda clan territory. Motoyasu was assigned a separate mission to capture the stronghold of Marune. As a result, he and his men were not present at the Battle of Okehazama where Yoshimoto was killed in Nobunaga's surprise assault.[7]^: 37

With Imagawa Yoshimoto dead, and the Imagawa clan in a state of confusion, Motoyasu used the opportunity to assert his independence and marched his men back into the abandoned Okazaki Castle and reclaimed his ancestral seat.[10] Motoyasu then decided to ally with Oda Nobunaga.[12] A secret deal was needed because Motoyasu's wife, Lady Tsukiyama, and infant son, Nobuyasu, were held hostage in Sunpu by Imagawa Ujizane, Yoshimoto's heir.[13]

In 1561, Motoyasu openly broke with the Imagawa and captured the fortress of Kaminogō. Kaminogō was held by Udono Nagamochi. Resorting to stealth, Motoyasu forces under Hattori Hanzō attacked under cover of darkness, setting fire to the castle, and capturing two of Udono's sons, whom he used as hostages to exchange for his wife and son.[11]^: 216

In 1563, Matsudaira Nobuyasu, the first son of Motoyasu, was married to Oda Nobunaga's daughter Tokuhime.

In February 1563, Matsudaira Motoyasu changed his name to Matsudaira Ieyasu.[14][15] For the next few years Ieyasu was occupied with reforming the Matsudaira clan and pacifying Mikawa. He also strengthened his key vassals by awarding them land and castles. These vassals included Ōkubo Tadayo, Ishikawa Kazumasa, Kōriki Kiyonaga, Sakai Tadatsugu, Honda Shigetsugu, Amano Yasukage and Hattori Hanzō.

During this period, the Matsudaira clan also faced a threat from a different source. Mikawa was a major center for the Ikkō-ikki movement, where peasants banded together with militant monks under the Jōdo Shinshū sect, and rejected the traditional feudal social order. Ieyasu undertook several battles to suppress this movement in his territories, including the Battle of Azukizaka (1564).[11]^: 216

An ukiyo-e print depicting the Battle of Batogahara. In his early days as daimyo of Mikawa, Ieyasu had difficult relations with the Jōdō Shinshū temples which escalated in 1563–1564.

On January 15, 1564, Ieyasu had decided to concentrate his forces to attack and eliminate the Ikkō-ikki from Mikawa. In the Ikkō-ikki ranks were some of Ieyasu's vassals, like Honda Masanobu and Natsume Yoshinobu, who had deserted him for the Ikkō-ikki rebellion out of religious sympathy.

Ieyasu was fighting in the front line and was nearly killed when struck by several bullets which did not penetrate his armour. Both sides were using the new gunpowder weapons which the Portuguese had introduced to Japan just 20 years earlier. At the end of battle, the Ikkō-ikki were defeated. By 1565, Ieyasu became master of all of Mikawa Province.

In 1567, Ieyasu started the family name "Tokugawa", finally making his name to Tokugawa Ieyasu. As he was a member of the Matsudaira clan, he claimed descent from the Seiwa Genji branch of the Minamoto clan. However, there was no proof the Matsudaira clan are descendants of Emperor Seiwa.[16] Yet, his surname was changed with the permission of the Imperial Court, after writing a petition, and he was bestowed the courtesy title Mikawa-no-kami (Lord of Mikawa) and the court rank of Junior 5th Rank, Lower Grade (從五位下, ju go-i no ge). Though the Tokugawa could claim some modicum of freedom, they were very much subject to the requests of Oda Nobunaga. Ieyasu remained an ally of Nobunaga and his Mikawa soldiers were part of Nobunaga's army which captured Kyoto in 1568. At the same time, Ieyasu was eager to expand eastward to Tōtōmi Province. Ieyasu and Takeda Shingen, the head of the Takeda clan in Kai Province, made an alliance for the purpose of conquering all the Imagawa territory.[17]^: 279

In 1569, Ieyasu's troops penetrated into Tōtōmi Province. Meanwhile, Takeda Shingen's troops captured Suruga Province (including the Imagawa capital of Sunpu). Imagawa Ujizane fled to Kakegawa Castle, which led to Ieyasu laying siege to Kakegawa. Ieyasu then negotiated with Ujizane, promising that if Ujizane should surrender himself and the remainder of Tōtōmi, Ieyasu would assist Ujizane in regaining Suruga. Ujizane had nothing left to lose, and Ieyasu immediately ended his alliance with Takeda, instead making a new alliance with Takeda's enemy to the north, Uesugi Kenshin of the Uesugi clan. Through these political manipulations, Ieyasu gained the support of the samurai of Tōtōmi Province.[10]

In 1570, Ieyasu established Hamamatsu as the capital of his territory, placing his son Nobuyasu in charge of Okazaki.[18]

In 1570, Azai Nagamasa, the brother-in-law of Oda Nobunaga, broke his alliance with the Oda clan during the siege of Kanegasaki. Soon Nobunaga was ready to punish Nagamasa for his treachery. Ieyasu led 5,000 of his men to support Nobunaga at the battle.[7]^: 62 The Battle of Anegawa occurred near Lake Biwa in Ōmi Province. The allied forces of Oda Nobunaga and Tokugawa Ieyasu defeated the combined forces of the Azai clan and Asakura clan, and saw Nobunaga's prodigious use of firearms. It is notable as the first battle that involved the alliance between Nobunaga and Ieyasu.

In October 1571, Takeda Shingen broke the alliance with the Oda-Tokugawa forces and now allied with the Odawara Hōjō clan. He decided to make a drive for Kyoto at the urgings of the shōgun Ashikaga Yoshiaki, starting with invading Tokugawa lands in Tōtōmi. Takeda Shingen's first objective in his campaign against Ieyasu was Nishikawa Castle, Yoshida Castle and Futamata Castle. In 1572, after besieging Futamata, Shingen would press on past Futamata towards the major Tokugawa home castle at Hamamatsu. Later, Ieyasu asked for help from Nobunaga, who sent him some 3,000 troops. Early in 1573 the two armies met at the Battle of Mikatagahara, north Hamamatsu. The considerably larger Takeda army, under the expert direction of Shingen, overwhelmed Ieyasu's troops and caused heavy casualties. Despite his initial reluctance, Ieyasu was convinced by his generals to retreat.[19][18] The battle was a major defeat, but in the interests of maintaining the appearance of dignified withdrawal, Ieyasu brazenly ordered the men at his castle to light torches, sound drums, and leave the gates open, to properly receive the returning warriors. To the surprise and relief of the Tokugawa army, this spectacle made the Takeda generals suspicious of being led into a trap, so they did not besiege the castle and instead made camp for the night.[19] This error would allow a band of Tokugawa soldiers to raid the camp in the ensuing hours, further upsetting the already disoriented Takeda army, and ultimately resulting in Shingen's decision to call off the offensive altogether. Takeda Shingen would not get another chance to advance on Hamamatsu, much less Kyoto, since he would perish shortly after the siege of Noda Castle later that same year.[12]^{: 153–156}

Shingen was succeeded by his less capable son Takeda Katsuyori. In 1574, Katsuyori took Takatenjin fortress. Then, in 1575, during Takeda Katsuyori's raid through Mikawa Province, he attacked Yoshida Castle and besieged Nagashino Castle. Ieyasu appealed to Nobunaga for help and Nobunaga came personally with 30,000 strong men. The Oda-Tokugawa forces of 38,000 won a great victory and successfully defended Nagashino Castle. Though the Takeda forces had been destroyed, Katsuyori survived the battle and retreated back to Kai Province.[20] For the next seven years, Ieyasu and Katsuyori fought a series of small battles, as the result of which Ieyasu's troops managed to wrest control of Suruga Province away from the Takeda clan.

In 1579, Lady Tsukiyama, Ieyasu's wife, and his heir Nobuyasu, were accused by Nobunaga of conspiring with Takeda Katsuyori to assassinate Nobunaga, whose daughter Tokuhime was married to Nobuyasu. For this reason, Ieyasu ordered his wife to be executed and forced his son to commit seppuku. Ieyasu then named his third son, Tokugawa Hidetada, as heir, since his second son had been adopted by Toyotomi Hideyoshi, who would later become an extremely powerful daimyo.

In 1580, Oda-Tokugawa forces launched the second siege of Takatenjin; the siege came only six years after Takeda Katsuyori had taken the fortress. This second siege lasted from 1580 until 22 March 1581, and ended with the deaths of 680 men in the Okabe Motonobu garrison and the fall of the fortress to the Oda-Tokugawa forces.

The end of the war with Takeda came in 1582 when a combined Oda-Tokugawa force attacked and conquered Kai Province. Takeda Katsuyori was defeated at the Battle of Tenmokuzan, and then committed seppuku.[11]^: 231

In late June 1582, before the incident at Honnō-ji temple, Oda Nobunaga invited Ieyasu to tour the Kansai region in celebration of the demise of the Takeda clan. When he learned that Nobunaga had been killed at the Honnō-ji temple by Akechi Mitsuhide, this meant that some provinces, ruled by Nobunaga's vassals, were ripe for conquest. Later, Ieyasu traveled back to Mikawa for gathering his forces. With the help of his retainer and ninja leader Hattori Hanzō, he escaped from Mitsuhide troops. Ieyasu first went through Sakai, then crossed the mountains of Iga Province, finally reaching the shore in Ise Province. He returned to his home Mikawa Province by sea. Ieyasu was mobilizing his army when he learned that Toyotomi Hideyoshi had defeated Akechi Mitsuhide at the Battle of Yamazaki.[17]^{: 314–315}

After the death of Oda Nobunaga at Honnō-ji temple, the lord of Kai Province made the mistake of killing one of Ieyasu's aides. Because of this, Ieyasu promptly invaded Kai and took control. Hōjō Ujimasa, leader of the Hōjō clan responded by sending his much larger army into Shinano Province and then into Kai Province. Later, both Ieyasu and the Hōjō clan agreed to a settlement which left Ieyasu in control of both Kai and Shinano provinces, while the Hōjō took control of Kazusa Province (as well as bits of both Kai and Shinano provinces).

In 1583, a war for rule over Japan was fought between Toyotomi Hideyoshi and Shibata Katsuie. Ieyasu did not take a side in this conflict, building on his reputation for both caution and wisdom. Hideyoshi defeated Katsuie at the Battle of Shizugatake. With this victory, Hideyoshi became the single most powerful daimyo in Japan.[17]^: 314

In 1584, Ieyasu decided to support Oda Nobukatsu, the eldest surviving son and heir of Oda Nobunaga, against Toyotomi Hideyoshi. This was a dangerous act and could have resulted in the annihilation of the Tokugawa clan, due to the fact that the Oda clan collapsed after Nobunaga's death.

Tokugawa troops took the traditional Oda stronghold of Owari. Hideyoshi responded by sending an army into Owari. The Komaki and Nagakute Campaign was the only time any of the great unifiers of Japan fought each other.

The Komaki and Nagakute Campaign proved indecisive and after months of fruitless marches and feints, Hideyoshi and Ieyasu settled the war through negotiations. First, Hideyoshi made peace with Oda Nobukatsu, and then he offered a truce to Ieyasu. The deal was made at the end of the year; as part of the terms Ieyasu's second son, Ogimaru (also known as Yuki Hideyasu) became an adopted son of Hideyoshi.

Ieyasu's aide, Ishikawa Kazumasa, chose to join the pre-eminent daimyo and so he moved to Osaka to be with Hideyoshi. However, few other Tokugawa retainers followed this example.

Toyotomi Hideyoshi was understandably distrustful of Ieyasu, and five years passed before they fought as allies. The Tokugawa did not participate in Hideyoshi's successful Invasion of Shikoku (1585) and the Kyūshū Campaign (1587).

In 1590, Toyotomi Hideyoshi attacked the last independent daimyo in Japan, Hōjō Ujimasa. The Hōjō clan ruled the eight provinces of the Kantō region in eastern Japan. Hideyoshi ordered them to submit to his authority and they refused. Ieyasu, though a friend and occasional ally of Ujimasa, joined his large force of 30,000 samurai with Hideyoshi's enormous army of some 160,000. The Odawara campaign was the first battle of Ieyasu and Hideyoshi as allies. They attacked several castles on the borders of the Hōjō clan with most of their army laying siege to the castle at Odawara. Hideyoshi's and Ieyasu's army captured Odawara Castle after six months (oddly for the time period, deaths on both sides were few). During this siege, Hideyoshi offered Ieyasu a radical deal: He offered Ieyasu the eight Kantō provinces which they were about to take from the Hōjō in return for the five provinces that Ieyasu currently controlled (including Ieyasu's home province of Mikawa). Ieyasu accepted this proposal. Bowing to the overwhelming power of the Toyotomi army, the Hōjō accepted defeat, their leaders committed suicide and Ieyasu marched in and took control of their provinces, ending the clan's reign of over 100 years.

The Sannohe faction of Nanbu clan led by Nanbu Nobunao organized a coalition of most of the factions of the Nanbu clan and pledged allegiance to Toyotomi Hideyoshi at the siege of Odawara. In return, he was recognized as chieftain of the Nanbu clan, and confirmed as daimyo of his existing holdings in the northern districts of Mutsu Province. However, Kunohe Masazane (1536–1591), lord of Kunohe Castle and leader of the Kunohe faction of Nanbu clan, felt that he had a stronger claim to the title of clan chieftain, and immediately rose in rebellion. In 1591, Hideyoshi and Ieyasu took the Kunohe Rebellion as a personal affront to Toyotomi authority and by mid-year organized a retaliatory army to retake northern Tōhoku and to restore the area to Nanbu Nobunao's control.

In 1591, Ieyasu now gave up control of his five provinces (Mikawa, Tōtōmi, Suruga, Shinano, and Kai) and moved all his soldiers and vassals to his new eight provinces at the Kantō region. He himself occupied the castle town of Edo in Kantō. This was possibly the riskiest move Ieyasu ever made—to leave his home province and rely on the uncertain loyalty of the formerly Hōjō samurai in Kantō. In the end however, it worked out brilliantly for Ieyasu. He reformed the Kantō region, controlled and pacified the Hōjō samurai and improved the underlying economic infrastructure of the lands. Also, because Kantō was somewhat isolated from the rest of Japan, Ieyasu ally with daimyo's of north east Japan like Date Masamune and Mogami Yoshiaki and he was able to maintain a unique level of autonomy from Toyotomi Hideyoshi's rule. Within a few years, Ieyasu had become the second most powerful daimyo in Japan. There is a Japanese proverb which likely refers to this event: "Ieyasu won the Empire by retreating."[21]

In 1592, Toyotomi Hideyoshi invaded Korea as a prelude to his plan to attack China. The Tokugawa samurai never actually took part in this campaign.

In 1593, Toyotomi Hideyoshi fathered a son and heir, Toyotomi Hideyori. Later, though in early 1593, Ieyasu himself was summoned to Hideyoshi's court in Nagoya (in Kyūshū, different from the similarly spelled city in Owari Province) as a military advisor and given command of a body of troops meant as reserves for the Korean campaign. Ieyasu stayed in Nagoya off and on for the next five years.[17] Despite his frequent absences, Ieyasu's sons, loyal retainers and vassals were able to control and improve Edo and the other new Tokugawa lands. However, the cost of the Japanese invasions of Korea significantly weakened the Toyotomi clan's power in Japan.

In 1598, with Toyotomi Hideyoshi's health clearly failing, Hideyoshi called a meeting that would determine the Council of Five Elders, who would be responsible for ruling on behalf of his son after his death. The five that were chosen as tairō (regent) for Hideyori were Maeda Toshiie, Mōri Terumoto, Ukita Hideie, Uesugi Kagekatsu, and Ieyasu himself, who was the most powerful of the five. This change in the pre-Sekigahara power structure became pivotal as Ieyasu turned his attention towards Kansai; and at the same time, other ambitious (albeit ultimately unrealized) plans, such as the Tokugawa initiative establishing official relations with New Spain (modern-day Mexico), continued to unfold and advance.[22][23]

Toyotomi Hideyoshi, after three more months of increasing sickness, died on September 18, 1598. He was nominally succeeded by his young son Hideyori but as he was just five years old, real power was in the hands of the regents. Over the next two years Ieyasu made alliances with various daimyo, especially those who had no love for Hideyoshi. Later, the oldest and most respected of the regents, Maeda Toshiie, died after just one year in 1599.

With the death of Toyotomi Hideyoshi in 1598 and Maeda Toshiie in 1599, Ieyasu led an army to Fushimi and took over Osaka Castle, the residence of Hideyori. This angered the three remaining regents and plans were made on all sides for war.

Opposition to Ieyasu centered around Ishida Mitsunari, one of Hideyoshi's Go-Bugyō, or top administrators of Hideyoshi's government and a powerful daimyo who was not one of the regents. Mitsunari plotted Ieyasu's death and news of this plot reached some of Ieyasu's generals. They attempted to kill Mitsunari but he fled and gained protection from none other than Ieyasu himself. It is not clear why Ieyasu protected a powerful enemy from his own men but Ieyasu was a master strategist and he may have concluded that he would be better off with Mitsunari leading the enemy army rather than one of the regents, who would have more legitimacy.[24]

Nearly all of Japan's daimyo and samurai now split into two factions—the Western Army (Mitsunari's group) and the Eastern Army (Ieyasu's group). Ieyasu supported the anti-Mitsunari group, and formed them as his potential allies. Ieyasu's allies were Katō Kiyomasa, Fukushima Masanori, Mogami Yoshiaki, Hachisuka Iemasa, the Kuroda clan, the Hosokawa clan and many daimyo from eastern Japan. Mitsunari allied himself with the three other regents: Ukita Hideie, Mōri Terumoto, and Uesugi Kagekatsu, as well as with Ōtani Yoshitsugu, Chosokabe clan, Shimazu clan and many daimyo from the western end of Honshū.

War became imminent when Uesugi Kagekatsu, one of Hideyoshi's appointed regents, defied Ieyasu by building up his military at Aizu. When Ieyasu officially condemned him and demanded that he come to Kyoto to explain himself, Kagekatsu's chief advisor, Naoe Kanetsugu, responded with a counter-condemnation that mocked Ieyasu's abuses and violations of Hideyoshi's rules, and Ieyasu was infuriated.

In July 1600, Ieyasu was back in Edo and his allies moved their armies to defeat the Uesugi clan, which they accused of planning to revolt against Toyotomi administration. On September 8, Ieyasu received information that Mitsunari had captured Fushimi castle and his allies had moved their army against Ieyasu. Ieyasu held a meeting with the Eastern Army daimyo, and they agreed to follow Ieyasu. Later on September 15, Mitsunari's Western army arrived at Ogaki Castle. On September 29, Ieyasu's Eastern Army took Gifu Castle. On October 7, Ieyasu and his allies marched along the Tōkaidō, while his son Hidetada went along through Nakasendō with 38,000 soldiers (a battle against Sanada Masayuki in Shinano Province delayed Hidetada's forces, and they did not arrive in time for the main Battle of Sekigahara). On October 20, Ieyasu's Eastern Army met Mitsunari's Western Army at Sekigahara, and on the following morning the battle began.

The Battle of Sekigahara was the biggest and one of the most important battles in Japanese feudal history. It began on October 21, 1600. Initially, the Eastern Army led by Tokugawa Ieyasu had 75,000 men, while the Western Army numbered 120,000 men under Ishida Mitsunari. Ieyasu had also snuck in a supply of arquebuses.

Knowing that the Tokugawa forces were heading towards Osaka, Mitsunari decided to abandon his positions and marched to Sekigahara. Even though the Western Army had tremendous tactical advantages, Ieyasu had already been in contact with many of the daimyo in the Western Army for months, promising them land and leniency after the battle should they switch sides, also having secretly communicated with Toyotomi Hideyoshi's nephew, Kobayakawa Hideaki. With a total of 170,000 soldiers facing each other, the Battle of Sekigahara ensued and ended with a complete Tokugawa victory.[25] Later, the Western bloc was crushed and over the next few days Ishida Mitsunari and many other western nobles were captured and killed. Tokugawa Ieyasu was now the de facto ruler of Japan.

Armor of Tokugawa Ieyasu at Kunōzan Tōshō-gū

Immediately after the victory at Sekigahara, Ieyasu redistributed land to the vassals who had served him. Ieyasu left some western daimyo unharmed, such as the Shimazu clan, but others were completely destroyed. Toyotomi Hideyori (the son of Hideyoshi) lost most of his territory which were under management of western daimyo, and he was degraded to an ordinary daimyo, not a ruler of Japan. In later years the vassals who had pledged allegiance to Ieyasu before Sekigahara became known as the fudai daimyō, while those who pledged allegiance to him after the battle (in other words, after his power was unquestioned) were known as tozama daimyō. Tozama daimyō were considered inferior to fudai daimyō.

From 1605, Ieyasu, acting as the retired shōgun (大御所, ōgosho), remained the effective ruler of Japan until his death. Ieyasu retired to Sunpu Castle in Sunpu, but he also supervised the building of Edo Castle, a massive construction project which lasted for the rest of Ieyasu's life. The result was the largest castle in all of Japan, the costs for building the castle being borne by all the other daimyo, while Ieyasu reaped all the benefits. The central donjon, or tenshu, burned in the 1657 Meireki fire. Today, the Imperial Palace stands on the site of the castle.[28]

In 1611, Ieyasu, at the head of 50,000 men, visited Kyoto to witness the enthronement of Emperor Go-Mizunoo. In Kyoto, Ieyasu ordered the remodeling of the Imperial Court and buildings, and forced the remaining western daimyo to sign an oath of fealty to him.

In 1613, he composed the Kuge shohatto (公家諸法度), a document which put the court daimyo under strict supervision, leaving them as mere ceremonial figureheads.[29]

In 1615, Ieyasu prepared the Buke shohatto (武家諸法度), a document setting out the future of the Tokugawa regime.[30]

William Adams before shogun Tokugawa Ieyasu

Letter from King James VI of Scotland and I of England and Ireland to ogosho Tokugawa Ieyasu in 1613

As Ōgosho, Ieyasu also supervised diplomatic affairs with the Netherlands, Spain, and England. Ieyasu chose to distance Japan from European influence starting in 1609, although the shogunate did still grant preferential trading rights to the Dutch East India Company and permitted them to maintain a "factory" for trading purposes.

From 1605 until his death, Ieyasu frequently consulted English shipwright and pilot, William Adams.[31] Adams, a Protestant[32] fluent in Japanese, assisted the shogunate in negotiating trading relations, but was cited by members of the competing Jesuit and Spanish-sponsored mendicant orders as an obstacle to improved relations between Ieyasu and the Roman Catholic Church.[33][34][35]

Significant attempts to curtail the influence of Christian missionaries in Japan date to 1587 during the leadership of Toyotomi Hideyoshi. However, in 1614, Ieyasu was sufficiently concerned about Spanish territorial ambitions that he signed a Christian Expulsion Edict. The edict banned the practice of Christianity and led to the expulsion of all foreign missionaries. Although some smaller Dutch trading operations remained in Nagasaki, this edict dramatically curtailed foreign trade and marked the end of open Christian witness in Japan until the 1870s.[36] The immediate cause of the prohibition was the Okamoto Daihachi incident, a case of fraud involving Ieyasu's Catholic vavasour, but the shogunate was also concerned about a possible invasion by the Iberian colonial powers, which had previously occurred in the New World and the Philippines.

Replica of Great Buddha of Kyoto build by Hideyori

The last remaining threat to Ieyasu's rule was Toyotomi Hideyori, the son and rightful heir to Hideyoshi.[3] He was now a young daimyo living in Osaka Castle. Many samurai who opposed Ieyasu rallied around Hideyori, claiming that he was the rightful ruler of Japan. Ieyasu found fault with the opening ceremony of a temple (Great Buddha of Kyoto) built by Hideyori; it was as if he prayed for Ieyasu's death and the ruin of the Tokugawa clan. Ieyasu ordered Hideyori to leave Osaka Castle, but those in the castle refused and summoned samurai to gather within the castle. Then in 1614, Tokugawa besieged the Osaka Castle against Hideyori.

Main tower of Osaka Castle

The Tokugawa forces, with a huge army led by Ieyasu and shōgun Hidetada, laid siege to Osaka Castle in what is now known as "the Winter Siege of Osaka". Eventually, the Tokugawa were able to force negotiations and an armistice after directed cannon fire threatened Hideyori's mother, Yodo-dono. However, once the treaty was agreed, the Tokugawa filled the castle's outer moats with sand so his troops could walk across. Through this ploy, the Tokugawa gained a huge tract of land through negotiation and deception that they could not through siege and combat. Ieyasu returned to Sunpu Castle, but after Toyotomi Hideyori refused another order to leave Osaka, Ieyasu and his allied army of 155,000 soldiers attacked Osaka Castle again in "the Summer Siege of Osaka".

Finally, in late 1615, Osaka Castle fell and nearly all the defenders were killed, including Hideyori, his mother (Toyotomi Hideyoshi's widow, Yodo-dono), and his infant son. His wife, Senhime (a granddaughter of Ieyasu), pleaded to save Hideyori and Yodo-dono's lives. Ieyasu refused and either required them to commit ritual suicide, or killed both of them. Eventually, Senhime was sent back to Tokugawa alive. With the Toyotomi line finally extinguished, no threats remained to the Tokugawa clan's domination of Japan.

• Sadler, A. L. (1937). The Maker of Modern Japan.