How did Wu Zetian destroy Goguryeo with millions of soldiers in Sui and Tang Dynasties?

Our predecessors planted trees, while our descendants enjoyed the cool. Two emperors, Li Shimin in Sui Dynasty and Tang Dynasty, weakened Goguryeo's national strength for Wu Zetian.

In fact, Wu Zetian didn't have any very awesome tricks to deal with Koguryo, because it was only a matter of time before Koguryo was destroyed. In order to eliminate Koguryo, the predecessors spared no effort to play their role. When Goguryeo was dying, this bargain happened to be picked up by Wu Zetian. At that time, Koguryo was not only short of national troops, but also short of food and grass, and was at a critical juncture of internal and external troubles. At this time, when the Tang Dynasty attacked and dispatched troops again, Goguryeo was powerless to fight back.

When Emperor Wendi of Sui Dynasty attacked Koguryo, although it was huge, the weather was bad and the losses were serious.

Emperor Wendi of Sui sent 300,000 troops to attack Koguryo, but they didn't pay attention to the weather when they attacked. As a result, they not only failed to win, but also lost most of the troops in the country. First, because it was rainy when they attacked, the transportation of grain and grass was not very smooth, which led to the interruption of grain and grass. Second, the rear reserves are insufficient and morale is low. Third, the Sui Dynasty water army suffered a big storm, which led to the total annihilation of the whole water army. Based on the above, the troops sent out were basically wiped out by God.

At the end of the Sui Dynasty, Yang Di was in a hurry and accomplished nothing.

The emperors of Sui Dynasty have realized the threat of Koguryo, so their emperors spared no effort to suppress Koguryo. Emperor Yang Di wanted revenge, but when he sent troops to attack Koguryo, his backyard caught fire. He had never won a battle before, but at the critical moment, something suddenly happened. Emperor Yang Di had to mind his own business first, so the attack was postponed indefinitely. He returned to the Sui Dynasty to deal with family affairs.

Li Shimin learned a lesson from the failure of the last dynasty. He changed his attack mode to hooliganism, and Koguryo's national strength was gradually consumed by the Tang Dynasty.

Li Shimin is very clever. He knows that Koguryo is a country that is easy to defend but difficult to attack. So it is convenient for Koguryo to fight a protracted war. He sends his own troops to harass Koguryo from time to time. Goguryeo can't take Li Shimin, so she can only defend the first world war, and her national strength is weakening day by day. Even a big fat man can't stand the bite of a mosquito all day long, so Koguryo's weakness is a trend!