Why did no one invade Japan during its Middle Ages?
1 Answer
They actually did
Explanation:
The Mongols attempted to invade Japan twice (1274, 1281), when Japan was under the Kamakura shogunate. They twice suffered terrible losses, both times, ironically, primarily due to typhoons, which destroyed the majority of the invading force.
However, the root of your question is, "why does no one invade Japan?", which is the same reason why not many people invade islands to begin with, especially during the Middle Ages.
A naval invasion implicates supplying troops, in the Middle Ages this would be extremely troublesome. Say, between China and Japan, lies a body of water which would (at the time) take quite a bit (to send supplies through). Not only are supplies a constant concern (especially for a huge landing force), but you also have to take into consideration reinforcements, and other such details. These take time, especially during the Middle Ages, and especially from China to Japan, thus making it wildly impractical to invade it in the first place.
Even if this did happen, coordination between armies was somewhat poor at the time, so even if the Mongols managed to establish a beachhead, it would give the Japanese enough time to consolidate a large enough force to either a) retaliate against the invading army, b) raids, c) make the scene for a decisive battle.
In the case of the Mongols, they invaded Kyushu (below), as you can see, Japan is also a very mountainous place, thus another hassle is to be included into the list as to why it is counter-intuitive to invade Japan.
At the time, Japan didn't really bother anyone, as they were embroiled in internal struggles for a better part of their history, thus the only reason as to why anyone would invade them is simply for the sake of conquest.
