The Great Wall is not a single wall but a series built by different Chinese dynasties.
Its fortifications began as separate walls built by rival states during the Spring and Autumn and Warring States periods. After Qin Shi Huang unified China in 221 BC, the Qin dynasty connected and extended some earlier defenses along the northern frontier. Later regimes repeatedly repaired, abandoned, rebuilt, or expanded different sections according to changing military needs.
The Han dynasty extended defenses westward, while the Northern dynasties, Sui, Jin, and other governments built their own frontier barriers. The Ming dynasty produced the best-known surviving sections, using large quantities of brick and stone and creating an extensive network of walls, trenches, passes, towers, and forts.
This is why “the Great Wall” is better understood as a long-lived defensive system than as one uninterrupted structure. Emperors ordered construction, and generals supervised campaigns, but neither term fits the sentence as precisely as “dynasties.” Provinces were administrative regions, and generals were commanders rather than the political periods responsible for successive building programs.