Complex sentence: Goguryeo cavalry forces, although outnumbered, overwhelmed the Chinese troops in combat and eventually emerged victorious.When Sui army had reached Salsu (thought to be present Cheongcheon river), the water level was shallow.
Split into simpler sentences: Goguryeo cavalry forces, although outnumbered, overwhelmed the Chinese troops in combat and eventually emerged victorious. When the Sui army had reached Salsu (thought to be present Cheongcheon river), the water level was shallow.