The Ming Dynasty was one of the famous dynasties in China, became recognised for its achievements like building the Great Wall and trade expansion. The Ming Dynasty also remembered for its drama, literature and world-renowned porcelain. During the Ming period, they struggled with neighbouring regions as Mongols which continued for decades. The Ming dynasty was able to maintain their northern border despite not winning the war. To overcome the problems with the Mongols, the Ming built the massive wall.
It occurred because it was cheaper and businesses could retain more money and underpay their workers. The practical reasons are that children are faster, they can fit into smaller spaces and are more controlled.