Goguryeo was a kingdom that ruled across the north and center of the Korean peninsula. Its territory extended into Manchuria, encroaching on Sui Dynasty territory. The Sui forces vastly outnumbered the Goguryeo. General Mondeok carried out a strategy. The goal was to repel Sui forces before retreating to the Salsu River, where the Goguryeo had set a trap. The river had been blocked, allowing the Sui to join the shallow water. When they did, the Goguryeo breached the dam and drowned a large number of Sui men. The remainder were readily vanquished. ¹⁾