Why did the Great Wall lose military importance during the Tang dynasty?

During the Tang dynasty (618–907), the Great Wall of China lost its military significance because the Chinese state grew significantly stronger in its military capabilities.1

Rather than relying on static fortifications, the Tang government successfully defeated the Tujue (a group of eastern Turks) in the north and expanded its territory well beyond the original frontier. Because the empire had effectively neutralized its primary northern threats and extended its reach, the wall was no longer required for defense, rendering further repairs or additions unnecessary during that period.1