What was the Siege of Osaka?
The Osaka campaigns were the last war of the Sengoku period. Tokugawa Ieyasu, already retired as shogun but still in control, destroyed the surviving Toyotomi house and its heir Toyotomi Hideyori in two campaigns fourteen years after Battle of Sekigahara.
They are also where Sanada Nobushige made the charge that turned him into a legend.
Why did it happen?
Sekigahara had left the Toyotomi in Osaka with a large castle, a substantial treasury and enormous symbolic weight. As long as Hideyori lived, any future crisis had an alternative centre of loyalty.
The pretext came in 1614. The Toyotomi had rebuilt a great temple in Kyoto, and the inscription cast on its new bell included characters that Tokugawa scholars declared to be a curse on Ieyasu's name. The reading was tendentious and the demands that followed were unacceptable, which was the point.
Tens of thousands of ronin — masterless warriors, many dispossessed after 1600 — converged on Osaka. For them it was the last chance to win back a place in the world.
Forces and sides
The Tokugawa fielded roughly 190,000–200,000 men. The defenders numbered around 90,000–100,000, the great majority of them ronin without a common command structure.
Osaka Castle was the strongest fortress in Japan, built by Toyotomi Hideyoshi on the site of a fortified temple complex that had held out against Oda Nobunaga for ten years.
What happened?
In the winter campaign of 1614 the Tokugawa surrounded the castle and found it could not be stormed. The Sanada Maru — a semicircular earthwork outwork built by Nobushige on the vulnerable southern approach — inflicted heavy losses on the units that attacked it.
Ieyasu turned to artillery and to negotiation. Cannon fire directed at the inner keep, and pressure through Hideyori's mother Yodo-dono, produced a truce. Its terms allowed the Tokugawa to fill in the outer moats. They filled in the inner ones as well, and demolished the outworks, before anyone could object.
When fighting resumed in the summer of 1615, Osaka was a castle without defences. The defenders had to fight in the open against a much larger army.
At Tennoji on 3 June 1615, Nobushige concentrated his men and drove straight at Ieyasu's command position. Tokugawa accounts record that the headquarters standard went down and the guard scattered — something that had not happened to Ieyasu since Mikatagahara. The charge was contained. Nobushige, exhausted, was killed shortly afterwards.
The castle fell the next day. Hideyori and Yodo-dono took their own lives in a burning storehouse.
Turning point
The winter truce. Filling in the moats was the decisive act of the whole war, and it was accomplished by negotiation rather than by fighting.
Outcome
The Toyotomi line ended. Hideyori's young son was executed; his daughter was placed in a convent. Surviving defenders were hunted down over the following weeks.
The Tokugawa immediately issued the laws that would define the next two centuries: one castle per domain, restrictions on daimyo marriages and building, and a code of conduct for the warrior houses. The era name was changed to Genna, and the settlement was called Genna Enbu — the laying down of arms.
Why it mattered
Osaka is where the Sengoku period ends. After 1615 there was no more large-scale warfare in Japan until the 1860s.
It is also where the samurai as a fighting profession begins to become the samurai as an administrative class. The tens of thousands of ronin who died at Osaka were men for whom the new order had no use, and they knew it.
