This Total War: Shogun 2 mod lets you play out the real historical war that inspired the FX TV show

pcgamer.com:

While PC gamers all over the place are flocking back to Fallout after having a great time watching the new Amazon TV series, I'm over here quietly despairing that there's only a single episode of FX's Shogun left to air. The new adaptation of the 1975 novel has been so excellent I even considered playing the 1980s PC games that tried to put their own spin on the story just like our news writer Joshua Wolens did, but then I came to my senses and went looking for options that aren't quite as old as computers with 64 kilobytes of RAM.

And I found the perfect one in the first place I looked: the Total War: Shogun 2 Steam Workshop.

The Sekigahara Campaign jumps Total War: Shogun 2's campaign forward in history approximately 50 years, to the 1590s. During the time period of the game's vanilla campaign starting in the 1540s, warlord Oda Nobunaga and his ally Tokugawa Ieyasu won a string of victories until he was betrayed and assassinated by his vassal Akechi Mitsuhide; not long after, Tokugawa allied with another of Nobunaga's allies, Toyotomi Hideyoshi, to quickly defeated Mitsuhide. The two would later be enemies and then allies again, and Hideyoshi would go on to unite Japan and end the «warring states» period of the last 100-odd years. The broad strokes of those events form the backdrop for James Clavill's novel, with all the major players having their names changed: 

The events of Total War: Shogun 2 let you play through the decades prior to the show and novel, then, but the Sekigahara Campaign jumps up to just before the events of the TV series. Should you choose to take command of the Tokugawa clan, you can lead the real-life version of Toranaga to victory. Or, instead, step into the shoes of Hidetoshi a few years prior to his death or control the clan of Toranaga's main rival from the council of regents in the show (Ishida Mitsunari is the real-life figure).

I installed the Sekigahara campaign with a click from the Steam Workshop and had no issue getting it