Why did Yang Di make three expeditions to Liaodong, and why did all three expeditions fail?

Yang Di's three visits to Liaodong are mainly due to Goguryeo's delay in obeying management, which may bring harm to the Yang Di dynasty. Therefore, Yang Di began to strike first, but all three expeditions to Liaodong failed because of overjoyed tactical command errors, which can be said to be the biggest failure in Yang Di's life.

Before Sui and Tang Dynasties, because I was busy with the Central Plains, I had no time to manage Liaodong area, so I gave it to some officials first. But later Koguryo developed slowly and its territory began to expand. Because they did not obey the management of the Central Plains Dynasty, they often occupied the land of local counties, and even in the Sui and Tang Dynasties, they began to repeatedly provoke the Central Plains Dynasty. In order to maintain the face of the dynasty and rectify Goguryeo, three wars were waged against it. But unfortunately, all three wars failed.

Yang Di's first expedition to Koguryo failed because Yang Di's mistakes in command and strategic judgment at that time led to the failure of a million troops in Liaodong War, instead of defeating a small Koguryo. After the defeat, Yang Di had planned to lead troops to recuperate and fight again after adjustment, but he was forced to fight at the front line at that time, and his own politics also went wrong. The soldiers who were in charge of escorting grain and grass suddenly defected. Yes, Emperor Yang Di wanted to fight while calming the war in the court. Later, the imperial war was pacified, and Yang Di killed many people, but Liaodong was still not captured.

Later, when I was well cultivated, I began my third expedition to Liaodong. The army was quite strong at that time. Later, King Goguryeo of Sui Dynasty was afraid that his country would be destroyed, so he sent messengers to make peace and hoped that Emperor Yang Di would spare himself. Emperor Yang Di was arrogant, and Goguryeo condescended to satisfy vanity, so he ordered the withdrawal and gave up the war.