Command of Sea Power in Northeastern Asia

The foundation of Chang Po-go's merchant fleets was spreaded across three regions. one was based on the people of Koguryo, Baekje, and Shilla, who had advanced early on to Shan Tong Peninsula and near a Great Canal region in China another was local residents and maritime power who were based on Wando island and Southwestern region of Korean Peninsula and the last one was the migrants of Baekje, Koguryo, and Shilla and a Japanese-Shilla community which was formed by Shilla people who moved to Japan from natural disaster.

After the establishment of Cheong-Hae-Jin, Chang Po-go's trading activity toward Japan set in full-scale force. The trading envoys that he sent to Japan were called 'Hoe-Yeok-Sa'(commissioner of trade), and they performed their trading activities under the approval of ‘Dajayhoo’(regional administrative office in Kyushu) and Japanese central government.

Remains discovered in Cheong-Hae-Jin(Wand-do Is.)

Chang Po-go's Cheong-Hae-Jin established an international network among Korea, China, and Japan through private trade and had an active trading relationship with Arabian merchants; it became an international maritime trading hub and grew into a maritime power that had military, administrative, and economic independence. Under his authority, Chang Po-go secured a strong position at Wando island which was the intermediary center of East Asia at that time and controlled trading routes. He accumulated considerable wealth and constructed a maritime Kingdom.