It's a because during the middle ages kingdoms conquer other nations by the numbers as soon as the child has education he (I say he because they didn't allow women to have education back then) he will enlist into one of the European nations and fight.
How Japanese Castles are similar to European Castles
1.They had large and tall walls for protection
2. They often had moats around them to discourage the digging of tunnels
3. They had narrow and steep stairways to make assault difficult
4. They had portholes for guns and for arrows
5. They often had a main gate area that could be used as a trap
6. They almost always had concentric rings of walls to give them multiple layers of protection
7.They capitalized on terrain features - often the best placement was at
the top of a hill or small mountain. This gave a very advantageous
position and view
DIFFERENCES
Unlike European feudalism Japan’s feudalism system did not have a true
pyramid form with the monarch presiding over the less important nobles.
First, the authority in Japan was much less centralized than it was in
the nation-states of Europe. Even though most of the local aristocrats
paid lip service to the emperor, the rugged terrain of Japan made it
very difficult for the emperor to fully control the local aristocracy.
Therefore the local aristocrats had much more power in Japan than they
ever had in France, Britain, or any other European country.
Secondly, even though the lower nobility in Japan (the samurai) swore
fealty to their local lords, the local lords didn’t give the samurai any
land of their own. When the European nobility receives land in exchange
for their military services, the samurai did not join a landowning
hierarchy. Instead of that they were given an independent income from
their local lord based upon what that lord’s lands produced.
In contrast, European knights usually had their own serfs to work the
land the knights received from their lord. While a Japanese samurai
might have had servants, these servants did not work the land the way
they would have done in Europe.
