Trade with Japan

After the unification of the Three Kingdoms, in Korean Peninsula, oversea trade with Japan was relatively smooth; but at the end of the 8th century, the trading relationship with Japan was cut off
 

Due to this severance of trading realtionship with Japan, private trading was
  increased whereas public trading was stopped.
At that time, Japanese nobles satisfied their desire for Chinses goods through the
  intermediary trade with Shilla merchants.
 
- In 768, Japanese government granted 70,000 tons of cotton as a trading payment
  to buy goods from Shilla for the princess, cabin members, high-ranking government
  officials.
- Some members of Japanese Envoys to Tang hired Korean translators an attempted
  to have relationship with Chang Po-go's Cheong-Hae-Jin in Korea and Shillabang at
  Tang.
 


Trading between Shilla and Japan

Trading with Japan flourished in the 9th century, by including Shilla people at
  Tang.
  Especially after establish Cheong-Hae-Jin, trading between the two countries was
  in full-scale.
Chang Po-go sent Commercial delegates called Hoi-Yeok-Sa, to Japan and
  Dajayihoo positioned a trading base at Hakada; he executed trading activities with
  approval of and Japanese government .
 
- Japan allowed changpogo's envoys to freely trade goods that they brought to
  Japan.
- Shilla merchants dispatched from Cheong-Hae-Jin traded at trading areas such as
  Tsushima Island, Iki Island, Heerado, Hakada, Nakado.
- There is no records proving that Chang Po-go went to Japan; but considering all
  the circumstances, there is possiblity that he went to Japan and contacted Chiku
  Zen Tai Shu.(Regional Governor of Chiku Zen)