The early wall construction is attributed to the first emperor of China, Tần Thủy Hoàng, who conquered the other states and unified China in 221 BC.
Tần Thủy Hoàng (259-210 BC) was an extraordinary man, a giant in his times, and it would be 
rash to deny him any of the supernatural powers with which he is 
credited.  He understood the dynamics of power.  He built an empire 
that lasted two millennia (221-210 BC), and a Wall that streches for thousands of 
miles.  Those are not an ordinary mortal's accomplishments.
Although the dynasty fell apart four years after his death, many aspects of its system of government endured 
in imperial China for more than 2,000 years.
Tần Thủy Hoàng was born Qin Zheng in Qin, a state in northern 
China.  At age 13, he succeeded his father, Qin Zichu, king of Zhuang Xiang, 
as ruler of the Qin state and took the title King Zheng (sometimes 
spelled Cheng). At the time he ascended the throne, Qin was the 
strongest of China's seven so-called Warring States, which were 
remnants of the Zhou (Chou) dynasty, a feudal regime that ruled China 
from around 1027 BC until 256 BC. Over the centuries, nobles had become 
rulers of independent kingdoms and had taken up arms against one 
another. Beginning in the 4th century BC, the Qin rulers who preceded 
King Zheng implemented reforms designed to strengthen the government of 
the Qin state. Military and administrative appointments, which had 
previously been determined by noble birth, were now decided by merit. 
Farmers, no longer enslaved servants, were allowed to own their land, 
and production increased. The Qin government strictly enforced laws 
issued by the rulers, and for this reason it is often described as 
Legalist.
Although King Zheng had ascended the throne in 247 BC, officials from 
his father's government continued to rule the Qin state until Zheng 
was declared of age in 238 BC. Upon assuming control, Zheng began 
planning the conquest of the other six states. In 230 BC Qin defeated 
Han, the weakest of the states, and within nine years it had conquered 
the others. 
In 221 BC King Zheng, having completed the unification of China by 
military force, proclaimed himself Qin Shihuangdi/Tần Thủy Hoàng Ðế (First Qin Emperor). 
As the first ruler to govern a truly unified China, Qin Shihuangdi 
imposed an extraordinary series of measures designed to reinforce the 
authority of the central government. A new system replaced feudal 
kingdoms with 36 (later 42) jun (provinces) that were run by appointed 
officials. To facilitate trade and communication, the government 
standardized weights and measurements and created a uniform writing system 
for the Chinese language. The regime maintained tight control over 
information by destroying books or removing them from circulation 
(books about agriculture, divination, and medicine were exceptions), 
and by putting hundreds of dissenting scholars to death. The government 
also built an extensive network of new roads and canals to improve 
communication and transportation. To protect China's northern frontier, 
the government constructed fortifications, thereby creating a 
precedent for the later network of walls that became known as the 
Great Wall (Vạn Lý Trường Thành).