Final answer:
The building of the Great Wall of China began in the Qin Dynasty, which lasted from 221 BCE to 206 BCE. Qin Shi Huang, the first emperor of the Qin Dynasty, united seven states and established a powerful central dynasty. The Great Wall of China was constructed during his reign as a defense against invading forces from the north.
Step-by-step explanation:
The building of the Great Wall of China began in Qin Dynasty, which lasted from 221 BCE to 206 BCE. The first emperor of the Qin Dynasty, Qin Shi Huang, united seven states and established a powerful central dynasty. During his reign, the Great Wall of China was constructed as a defense against invading forces from the north.