While no records of Chang 's childhood are extant, he was probably born on Wando Island or in its vicinity in the second half of the 8th century, spending his childhood there. It is thought that he was born on Cheonghaejin (now Wando) in the late 780s. He was a strong and robust young man who was good at archery with a ready use of the spear.
Chang activities in China
(As Junior Commander for Mooryeonggun) In China (Tang Dynasty), Chang rendered distinguished services in the Mooryeonggun army. At age 30 (819), he became the junior commander for Mooryeonggun with about 1,000 troops.
Chang activities in China (Jeoksan Beophwawon established)
After retiring as Junior Commander for Mooryeonggun, Chang established Beophwawon in Jeoksanpo, Shandong Peninsula. His diverse activities had an influence on the Silla people in China. A Japanese monk, Ennin, wrote a letter to ChangPoGo asking for assistance in returning to Japan while he was in Beophwawon, which highlights Chang high status in international society.
Kidnapping of innocent people by pirates
In the early 9th century, the open seas were infested with pirates. Taking advantage of an instable political situation, they would often be seen along the coasts of Silla. ChangPoGo, living in Tang China at the time, was shocked by these tragic incidents
Meeting with King Heungdeok and ridding the sea of pirates
After returning to Korea from China, ChangPoGo met with King Heungdeok and was granted permission to establish Cheonghaejin with 10,000 troops. He swept the sea route between Silla and Tang Dynasty clear of marauders. In a short period of time, Chang greatly expanded his power in the sea by uniting small maritime powers and securing maritime trade rights.
Establishment of Cheonghaejin | The naval and maritime trade base in the East Asia - Cheonghaejin
Cheonghaejin was established in 828 (the 3rd year of King Heungdeok's reign). Chang pioneered maritime trade under the philosophy of "the one who rules the ocean will rule the world." He opened a major sea route to connect Korea, China and Japan. Based in Cheonghaejin, Chang launched intermediary trade that linked both China and Japan and was Asia's first private entrepreneur to begin trade with Muslims.
Cultural exChang e activities
With strategic bases in China and Japan, Cheonghaejin became the base for maritime trade among Korea, China and Japan. The ChangPoGo Fleet expanded its influence to the southern part of China and launched trade with Arabia. Chang brought Islamic porcelain and glassware to Silla and Japan, making an enormous fortune by trading these exotic goods. Chang was, ultimately, the king of maritime trade in Northeast Asia.
Contention for the throne in the Silla and the Assassination of ChangPoGo
With the establishment of Cheonghaejin, ChangPoGo ruled the maritime world but to his misfortune became involved in the contention for the throne of the Silla Dynasty. In 839, Chang sent 5,000 troops to Gyeongju to defeat the political opponents of U-Jing Kim, allowing Kim to become king of Silla (King Sinmu). Upon obtaining the throne, the royal family including the king himself began a check of ChangPoGo's power. In the end, Yeom Jang, who once was a loyal subordinate of ChangPoGo, assassinated Chang on the king's orders in 841.