right ... but I have to get SOME version of Empire Total War before getting Napoleon right? or can I buy/install Napoleon as a standalone?
And furthermore, the mongols invaded Japan in the late 1200s, and sometime before or after giver or take 100 years, was when Japan attempted to invade Korea and failed horribly. China and Japan never fought before the Meiji restoration, when Japan kicked Korea's Ass, Russia's Ass, and was starting to take names, and face down China herself. That was late 1800s, like 1890 - 1920.
As far as the 1500s, this was when Japan was looking inward, only fighting among each other. The only outside influence was limited trade with China, Korea, Portugal, and the Dutch. The latter two was where Japan gained the knowledge of firearms from ... however some sort of law prevented further research to make BETTER firearms ... therefore Japan was stuck with 1500s based firearms until the late 1800s when their isolation (and stagnation/ peace n prosperity) came to a close.
Therefore it is fitting that this version of Shogun: Total war, taking place in the 1500s, is simply an internal struggle within Japan ... as historically the winner of the battle Tokugawa Ieyasu, in 1603, decided to close off Japan from foreign influence. Of note, he kicked out any and all Dutch/Portuguese immigrant missionaries, and pretty much put all Japanese Christians to death. That pretty swiftly ended Western Influence (or any foreign influence) in Japan, until Commodore Perry's Gunboat Diplomacy in the latter half of the 1800s.
During the Tokugawa Shogunate, 1603 - 1868, there was peace, agricultural revolution/transformation (45% MORE arable land), and general prosperity. This meant that the Arts were expanded upon, peace-time commercial avenues were expanded, and there was a greater sense of urbanization/ cities grew larger, more population. However, two things didn't happen which are relatively related. There was no combat/conflict during this era, and there was no advancement in weaponry effectiveness. Additionally, there was no technological advancements of any kind. The only advancements were to bring more people into the cities, have more farmland and better ways to farm, and increase proficiency in peacetime activities like literature, drama, painting, and other forms of art.
Edit: OR IN OTHER WORDS ....
The era of Mongol domination was already over, Kublai Khan (and Genghis Khan) were already dead, China and Korea were still minor trading partners but were becoming more and more ignored ... etc. Although, I suppose it would be fun to invade either Korea/Manchuria or mainland China after establishing complete Supremacy over the Japanese people. However ... the endless Chinese ... how can you fight so many?