The Warring States Period ( 战国时期 ) takes place from sometime in the 5th century BC to the unification of China by Qin in 221 BC. The date for the beginning of the Warring States Period is somewhat in dispute. While it is frequently cited as 475 BC, following the Spring and Autumn Period, 403 BC, the date of the tripartition of the State of Jin , is also sometimes considered as the beginning of the period. It is nominally considered to be the second part of the Eastern Zhou Dynasty, following the Spring and Autumn Period. Like the Spring and Autumn Period, the king of Zhou acted merely as a figurehead.

The Warring States Period, in contrast to the Spring and Autumn Period, was a period when regional warlords annexed smaller states around them and consolidated their rule. The process began in the Spring and Autumn Period, and by the 3rd century BC, seven major states had risen to prominence. These Seven Warring States ( 战国七雄 ), were the Qi ( 齐 ), the Chu ( 楚 ), the Yan ( 燕 ), the Han ( 韩 ), the Zhao ( 赵 ), the Wei ( 魏 ) and the Qin ( 秦 ).

The proliferation of iron working in China was seen by the Warring States Period, replacing bronze as the dominant metal used in warfare. Areas such as Shu and Yue were also brought into the Chinese cultural sphere during this time. Walls built by the states to keep out northern nomadic tribes and each other were the precursors of the Great Wall ( 长城 ) of China. Different philosophies developed into the Hundred Schools of Thought ( 百家争鸣 ) , including Confucianism ( 儒家思想 elaborated by Mencius), Taoism ( 道家思想 elaborated by Zhuang Zi), Legalism ( 法家思想 formulated by Han Feizi) and Mohism ( 墨家思想 formulated by Mozi). Military tactics also changed. Unlike the Spring and Autumn Period, most armies in the Warring States Period made combined use of infantry and cavalry, and the use of chariots gradually fell into disfavor.This was also around the time legendary military strategist Sun Wu ( 孙武 ) wrote The Art of War ( 孙子兵法 ) which is recognized today as the most influential, and oldest known military strategy guide.

In 403 BC, the three major families of Jin, with the approval of the Zhou king, partition Jin into three states: the State of Han , the State of Zhao , and the State of Wei . The three family heads were given the title of Marquess ( 侯 ). The State of Jin continued to exist with a tiny piece of territory until 376 BC when the rest of the territory was partitioned by the Three Jins.

In 371 BC, Marquess Wu of Wei passed away without specifying a successor, causing Wei to fall into an internal war of succession. After three years of civil war, Zhao and Han, sensing an opportunity, invaded Wei. On the verge of conquering Wei, the leaders of Zhao and Han fell into disagreement on what to do with Wei and both armies mysteriously retreated. As a result, King Hui of Wei was able to ascend onto the throne of Wei.

In 354 BC, King Hui of Wei initiated a large scale attack at Zhao. By 353 BC , Zhao was losing badly, and one of their major cities--Handan ( 邯郸 ), a city that will eventually become Zhao's capital--was being besieged. As a result, the neighbouring State of Qi decided to help Zhao. The strategy Qi used, suggested by the famous tactician Sun Bin ( 孙膑 ), who at the time was the Qi army advisor, was to attack Wei's territory while the main Wei army is busy sieging Zhao, forcing Wei to retreat. The strategy was a success; the Wei army hastily retreated, and encountered the Qi midway, culminating into the Battle of Guiling ( 桂陵之战 ) where Wei was decisively defeated. The event spawned the famous phrase " 围魏救赵 ", meaning attacking Wei to save Zhao.

In 341 BC, Wei attacked Han, and Qi interfered again. The two generals from the previous Battle of Guiling met again, and due to the brilliant strategy of Sun Bin, Wei was again decisively defeated at the Battle of Maling ( 马陵之战 ).

The situation for Wei took an even worse turn when Qin, taking advantage of Wei series of defeats by Qi, attacked Wei in 340 BC under the advice of famous Qin reformer Shang Yang ( 商鞅 ). Wei was devastatingly defeated and was forced to cede a large portion of its territory to achieve a truce. This left their capital Anyi vulnerable, so Wei was also forced to move their capital to Daliang.

After these series of events, Wei became severely weakened, and the Qi and Qin became two of the dominant states in China .

In 334 BC , the rulers of Wei and Qi agreed to recognize each other as Kings, formalizing the independence of the states and the powerlessness of the Zhou throne since the beginning of the Eastern Zhou Dynasty . The King of Wei and the King of Qi joined the ranks of the King of Chu , whose predecessors had been Kings since the Spring and Autumn Period . From this point on, all the other states eventually declare their Kingship, signifying the beginning of the end of the Zhou Dynasty.

Towards the end of the Warring States Period, the State of Qin became disproportionately powerful compared to the other six states. As a result, the policies of the six states became overwhelmingly oriented towards dealing with the Qin threat, with two opposing schools of thought: Hezong ( 合纵 ) ; and Lianheng ( 连横 ) , or alliance with Qin to participate in its ascendancy. There were some initial successes in Hezong, though it eventually broke down. Qin repeatedly exploited the Lianheng strategy to defeat the states one by one. During this period, many philosophers and tacticians travelled around the states recommending the rulers to put their respective ideas into use. These "lobbyists" were famous for their tact and intellect, and were collectively known as Zonghengjia ( 纵横家 ), taking its name from the two main schools of thought.