• We have updated our Community Code of Conduct. Please read through the new rules for the forum that are an integral part of Paradox Interactive’s User Agreement.
there have been 2-3 threads about this already; so far it looks like there won't be any foreign invasions (as in troop landings in Japan), although I understand there are foreign influences.
 
I think there shouldn´t be any foreign invasions in the game. I think the most probable invader would have been Spain from the Phillippines. The Dutch and the Portuguese didn´t have enough troops or cash to start a large scale military adventure in Japan. Korea wasn´t very militaristic nation then and it would have required a large navy to transport Korean troops to Japan. China was turned inside and she didn´t want to build a large navy for that kind of enterprise.

However, let´s see what would have happened in Japan during the Sengoku Jidai era if there would have been a foreign invasion. Japanese learned men still remembered the Mongol invasions during 13th century and the kamikaze. It would have been very likely that most of the Japan would have unified to fight against the invaders even if the invaders would have some allies among daimyos. One should remember that during the Sengoku Jidai era the leading daimyos were able to raise quite large armies with size of tens of thousand mens.

In 1560, Imagawa Yoshimoto planned to attack from fief at Totomi and Suruga(at the Southern Coast of Honshu between Kyoto and Tokyo) to Kyoto which was the capital. It is estimated that Imagawa´s army had from 15K to 35K men. His army was ambushed by Oda Nobunaga who led 1.5K in a surprise attack and his forces were able to kill Imagawa at Okehazama in 1560. Both Tokugawa Ieyasu and his opponents had each 80K men at the battle of Sekigahara in 1600. So, in the end, if someone would like to conquer the Sengoku Jidai era Japan by using 16th and 17th century era technology that someone should have hundreds of thousands of troops and, the means to land those forces to Japanese soil and keep them supplied as well. Anyway, that kind of invasion would change the game and it mechanics a lot and after that it wouldn´t be a traditional Sengoku Jidai game.