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What if the Korean kingdom of Balhae discovered Sakhalin following its northrn expansion?

Dae Insu, also known as King Seon (r. 818-830) was the 10th king of the Korean kingdom of Balhae. He restored national strength, and is remembered today as the last of the great Balhae rulers before its fall.

He reigned for 12 years and expanded the borders of Balhae to Primorsky Krai with intention of absorbing the Mohe, and Malgal peoples.

What if in the 10th year of his reign he learned of Sakhalin from coastal peoples(possibly Tartars or Nivks) and sent a ship to find, subjugate, and establish a fort on the island which a force of 100 succeed in doing?

Post King Seon

Balhae continues to build several more forts and four towns are started. The Balhaeans start to get tribute from the Ainu, Nivks and Ovorks and begin a process of absorbing them as well like the Mohe.

How this affect east asian history? Will it affect the fall of Balhae?
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