closed-door policy

Past the middle of the 19th century  around the end of the era of the samurai.
More than 200 years，Japan had banned exchanges with foreign countries as a national policy.
It called ”Sakoku”.  
　
This policy was conducted primarily as a guard against the West.
Era was the Age of Exploration as a matter of fact without good or bad.
For example，I think information of the Inca Empire of South America was coming to Japan.
　
But samurai government decided to abandon Sakoku  policy because there is pressure from western countries in 1854.
I think this was natural correspondence seen from the state of the world at the time.
(Days of sail was past.）


"The Western world was era of after the Industrial Revolution already.
If did not abandon this Sakoku policy here, it's the gap between Japan and the Western world would had open more and more.
Japan was able to catch up to the Western world because Sakoku policy abandoned at this point."

I remember idly heard so in college classes.

If they had just one wrong move, it was became too late surely.

・・・・・・・・・

At the time Japan was coalition Kingdom of samurai so to speak.
That leader position was Tokugawa clan.
There were many samurai countries in Japan called ”Three hundred lords”.
And some countries in it had been considered as a potential enemy from Tokugawa clan.
Their representatives was ”Satsuma” (Shimazu clan) and ”Choshu” （Mouri clan）.
　
Tokugawa hegemony had been established in win of this Battle of Sekigahara in 1600.
All samurai in Japan participated in this battle and they battled divided to ”East armed forces” and ”West armed forces”.
East armed forces was wins，then countries of West armed forces was almost destroyed.
　
Representatives of West armed forces was Satsuma and Choshu.
Until then, they were colleagues of equivalent position of Tokugawa clan.
They were not destroyed but They became vassal of Tokugawa clan after defeated at this battle.
　
Mouri clan territory was reduced to 3/1.
Incidentally Mouri clan began to popularly called Choshu (region name) after this.