Why did Genghis Khan attack Japan?

It is said that Genghis Khan attacked Japan because Japan refused to submit to him.

Genghis Khan sent messengers to Japan many times to persuade the Japanese to surrender to him, but the Japanese simply ignored him and even taught the messengers a lesson. Genghis Khan was dissatisfied with the Japanese's contempt for his majesty, so Genghis Khan wanted to send troops to attack Japan. So he sent nearly 30 thousand troops to Japan, divided into three ways and attacked from three places at the same time.

Extended data:

In the face of the Mongolian army's attack, the Japanese army took it easy. Japan's Kamakura shogunate mobilized some regular troops to fight against the Mongolian army, and the governors along the coast of Kyushu also urgently organized warriors and militia to participate in the war. The war lasted for nearly a month. At the beginning of the war, Japan was defeated and suffered heavy losses, but with their perseverance, the Mongolian army still did not go further.

Slowly, the Japanese began to fight back after getting familiar with the Mongolian fighting style, which was also an important turning point for the Japanese. 1June 20, 274, heavy rain struck, and Mongols were unfamiliar with the terrain, causing most ships to hit the rocks. At this point, the reinforcements were damaged by more than half. Genghis Khan saw that there was no hope of victory and ordered the rest of the troops to return the same way.