Geographical Environment and Political Game in Northeast Asia in Sui and Tang Dynasties –With Focus on the Military Operations of Eastern Expeditions

From a geopolitical point of view, the military operations of Eastern Expeditions in the Sui and Tang Dynasties were actually military and political games by players from the mainland, borderland and sea islands, represented by Sui and Tang Dynasties, Koguryo and Japan respectively. The Korean peninsula and its surrounding seas was the strategic center of Northeast Asia, the southwest of the peninsula, the Yellow Sea and the Tsushima Strait were the strategic pivot, and Paekehe once occupied the strategic key position of borderland area. Not until the maritime military strength of the Tang Dynasty was adequately enhanced to bring Paekehe under control did the Eastern Expeditions make its strategic breakthrough. This indicates that sea power cast decisive strategic influence and played an important role in the geopolitical environment of Northeast Asia.