B.C. 1766 - 1122 -- Kings and nobles from the Shang dynasty rule northern China. (A dynasty is a succession of rulers from the same family.)

B.C. 1122 - 771 -- The Zhou from western China overthrow the Shang.

B.C. 777 - 221 -- China breaks up into seven large states; most states are under the rule of the Zhou dynasty. The seven separate kingdoms are constantly at war with one another. Each state builds walls along its borders as a defense against enemies.

B.C. 221 -- Qin Shi Huangdi, ruler of the western state of Qin, conquers the seven major states and becomes the first emperor of a united China.

B.C. 214 -- Continual invasions and wars with the barbarians to the north drive the emperor to order the construction of the Great Wall to protect China. Qin Shi Huangdi uses 300,000 laborers to connect a number of the existing defensive walls into a Great Wall fortified by a system of watchtowers.

B.C. 202 - A.D. 220 -- The Han dynasty takes power and turns China into a strong empire. The Han dynasty rebuilds and extends the Great Wall.

A.D. 220 - 581 -- The Han dynasty falls, and there is widespread revolt. China breaks up into smaller dynasties. These dynasties continue making repairs and modifications on the Great Wall.

A.D. 581 - 617 -- China is reunified in 589 by the Sui dynasty. The Sui dynasty builds and repairs sections of the Great Wall.