Why did Ming rulers repeatedly repair and strengthen the Great Wall?

During the Ming dynasty (1368–1644), rulers ceaselessly maintained and strengthened the Great Wall of China primarily to prevent further Mongolian invasions.1

Following the collapse of the Yuan dynasty, which had been established by the Mongols, the Ming emperors viewed the Mongols as subjects and sought to secure their northern frontier against intermittent attempts by Mongol clans to regain their former power. This defensive strategy was critical for protecting the Ming capital, Beijing, which was located near key strategic passes such as Juyong, Daoma, and Zijing. These areas were typically heavily garrisoned to ensure the safety of the empire.21

The necessity for these fortifications was underscored by ongoing military threats, including the 1449 campaign by the Oirat leader Esen Taiji, who captured a Ming emperor and besieged Beijing. Consequently, the wall served as a vital barrier to maintain stability and protect the dynasty's political center from northern incursions.132