The sea trade route to the Sandung peninsular during the united Shilla period was stretched from the middle western coast of the Korea peninsular to a northwestern direction. However, traders had to turn their path to west at Ongjin or Pungju after passing the Haeju area by land since the establishment of the Goryeo dynasty. This is because Hubaekje navy could raid the traders who sailed from Gaegyeong, the capital city of Goryeo, along the southern coast of Hwanghae-do. It is considered that Goryeo sea traders were the major player of the sea trade route, actively trading in the Sandung region. The Haeju region became a strategical point as the route to the Sandung peninsular became critical for foreign affairs and trade. This is the reason of why Pungju and Ongjin, the ports of the Korean peninsular connected to the Sandung peninsular, Haeju, the path from Ongjin to Gaegyeong, and Yeomju and Baeju were in the Gyesookwan district of Haeju. On the other hand, Chinese traders mainly used the sea trade route that links the Yangtze river area to the southwestern sea of the Korea peninsular. As they established diplomatic relationship with both of Goryeo and Hubaekje, they passed through the Hubaekje territory to Goryeo. The Wunju coast located at the western coast of Chungcheong-do was a place where Goryeo and Hubaekje tried to have their domination in the southernwest route of the Korean peninsular at the early stage of the Goryeo period. If Hubaekje succeeded to take hold the region, Goryeo could not connect with the Naju area. If Goryeo succeeded to take hold the region, Hubaekje had to suffer from communicating with Chinese dynasties in the central China or the Kitan. Therefore, the two nations fought intensively for the domination of the region, and some of the battles were led by the Kings of the nations. Finally, Goryeo took over the region, and this helped Goryeo unite the Korea peninsular much.

The sea trade route to the Sandung peninsular during the united Shilla period was stretched from the middle western coast of the Korea peninsular to a northwestern direction. However, traders had to turn their path to west at Ongjin or Pungju after passing the Haeju area by land since the establishment of the Goryeo dynasty. This is because Hubaekje navy could raid the traders who sailed from Gaegyeong, the capital city of Goryeo, along the southern coast of Hwanghae-do. It is considered that Goryeo sea traders were the major player of the sea trade route, actively trading in the Sandung region. The Haeju region became a strategical point as the route to the Sandung peninsular became critical for foreign affairs and trade. This is the reason of why Pungju and Ongjin, the ports of the Korean peninsular connected to the Sandung peninsular, Haeju, the path from Ongjin to Gaegyeong, and Yeomju and Baeju were in the Gyesookwan district of Haeju. On the other hand, Chinese traders mainly used the sea trade route that links the Yangtze river area to the southwestern sea of the Korea peninsular. As they established diplomatic relationship with both of Goryeo and Hubaekje, they passed through the Hubaekje territory to Goryeo. The Wunju coast located at the western coast of Chungcheong-do was a place where Goryeo and Hubaekje tried to have their domination in the southernwest route of the Korean peninsular at the early stage of the Goryeo period. If Hubaekje succeeded to take hold the region, Goryeo could not connect with the Naju area. If Goryeo succeeded to take hold the region, Hubaekje had to suffer from communicating with Chinese dynasties in the central China or the Kitan. Therefore, the two nations fought intensively for the domination of the region, and some of the battles were led by the Kings of the nations. Finally, Goryeo took over the region, and this helped Goryeo unite the Korea peninsular much.

the Goryeo period, Hubaekje, King Taejo, Sea Route to China, Foreign Affairs, Trade, the Seohae