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 (戰國七雄/战国七雄 Zhànguó Qīxióng, literally "Seven Hegemonial among the Warring States"), were the Qi (齊/齐), the Chu (楚), the Yan (燕), the Han (韓/韩), the Zhao (趙/赵), the Wei (魏) and the Qin (秦). Another sign of this shift in power was a change in title: warlords once considered themselves dukes (公 gōng) of the Zhou dynasty king; but now the warlords began to call themselves kings (王 wáng), meaning they were equal to the Zhou king.
The Warring States Period saw the proliferation of iron working in China, replacing bronze as the dominant metal used in warfare. Areas such as Shu (modern Sichuan) and Yue (modern Zhejiang) were also brought into the Chinese cultural sphere during this time. Different philosophies developed into the Hundred Schools of Thought, including Confucianism (elaborated by Mencius), Taoism (elaborated by Lao Zi and to a lesser extent Zhuang Zi, in that it is possible to see the philosophy espoused in the text of the Zhuang Zi as separate from what could be considered "classical Daoism"), Legalism (formulated by Han Feizi) and Mohism (formulated by Mozi). Trade also became important, and some merchants had considerable power in politics. 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. Thus from this period on, the nobles in China remained a literate rather than warrior class, as the kingdoms competed by throwing masses of soldiers against each other. Arms of soldiers gradually changed from bronze to unified iron arms. Dagger-axes were an extremely popular weapon in various kingdoms, especially for the Qin who produced eighteen-foot long pikes.
This was also around the time the legendary military strategist Sun Tzu (Sun Zi) wrote The Art of War which is recognized today as the most influential, and oldest known military strategy guide. Along with this are other military writings that make up the Seven Military Classics of ancient China: T'ai Kung's Six Secret Teachings, The Methods of the Sima, Sun Bin's Art of War, Wu Qi, Wei Liaozi, Three strategies of Huang Shigong, and The Questions and Replies of Tang Taizong and Li Weigong (the last being made ±800 years after this era ended). Once China was unified, these seven military classics were locked away and access was restricted due to their tendency to promote revolution.
In the Spring and Autumn Period, the State of Jin (晉) was arguably the most powerful state in China. However, near the end of the Spring and Autumn Period, the power of the ruling family weakened, and Jin gradually came under the control of six ministers belonging to six different families (六卿). By the beginning of the Warring States Period, after numerous power struggles, there were four families left: the Zhi (智) family, the Wei (魏) family, the Zhao (趙) family, and the Han (韓) family, with the Zhi family being the dominant power in Jin. Zhi Yao (智瑶), the last head of the Zhi family, attempted a coalition with the Wei family and the Han family to destroy the Zhao family. However, because of Zhi Yao's arrogance and disrespect towards the other families, the Wei family and Han family secretly allied with the Zhao family, and the three families launched a surprise attack at Jinyang, which was besieged by Zhi Yao at the time, and annihilated the Zhi.
In 403 BC, the three major families of Jin, with the approval of the Zhou king, partitioned Jin into three states, which was historically known as 'The Partition of Jin of the Three Families' (三家分晉). The new states were: the State of Han, the State of Zhao, and the State of Wei. The three family heads were given the title of Marquis (侯), and because the three states were originally part of Jin, they are also referred to as the Three Jins (三晉). 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 389 BC, the Tian (田) family seized control of the State of Qi, and were given the title of Duke. The old Jiang (姜) family's State of Qi continued to exist with a small piece of territory until 379 BC, when it was finally absorbed into Tian family's State of Qi.
In 371 BC, Marquess Wu of Wei died 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 (still a Marquess at the time) was able to jump onto the throne of Wei.
In 354 BC, King Hui of Wei initiated a large scale attack at Zhao, which some historians believe was to avenge the earlier near destruction of Wei. By 353 BC, Zhao was losing the war badly, and one of their major cities — Handan (邯鄲/邯郸), a city that would 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 (孫臏/孙膑), a descendant of Sun Tzu, 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 (Pinyin: guì líng) (桂陵之戰/桂陵之战) where Wei was decisively defeated. The event spawned the idiom "圍魏救趙/围魏救赵", meaning "Surrounding Wei to save Zhao", which is still used in modern Chinese to refer to attacking an enemy's vulnerable spots in order to relieve pressure being applied by that enemy upon an ally.
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 (馬陵之戰/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.
Around 359 BC, Shang Yang (商鞅), a minister of the State of Qin, initiated a series of reforms based on the political doctrine of Legalism that transformed Qin from a backward state into one that surpasses the other six states. It is generally regarded that this is the point where Qin started to become the most dominant state in China.
Chu rose to its peak in 334 BC, when it gained vast amounts of territory. The series of events leading up to this began when Yue (越) prepared to attack Qi. The King of Qi sent an emissary who persuaded the King of Yue to attack Chu instead. Yue initiated a large scale attack at Chu, but was devastatingly defeated by Chu's counter-attack. Chu then proceeded to conquer the State of Yue. This campaign expanded the Chu's borders to the coasts of the Pacific Ocean.
The folkloric figure, Qu Yuan figures into this historical period, as a minister in the court of the King of Chu. [Refer to Duan Wu Festival]
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 (合縱/合纵 pinyin: hézòng, "vertically linked"), or alliance with each other to repel Qin expansionism; and Lianheng (連橫/连横 pinyin: liánhéng, "horizontally linked"), 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 (縱橫家), taking its name from the two main schools of thought.
Around 300 BC, Qi was almost totally annihilated by a coalition of five states led by Yue Yi of Yan (Qin were among those five). Although under General Tian Dan Qi managed to recover their lost territories, it would never be a great power again. Yan was also too exhausted afterwards to be of much importance in international affairs after this campaign.
In 278 BC, Qin attacked Chu and managed to capture their capital city, Ying, forcing the Chu king to move eastwards to Shouchun. This campaign virtually destroyed Chu's military might, although they recovered sufficiently to mount serious resistance against Qin 50 years later.
In 260 BC, the Battle of Changping was fought between Qin and Zhao, resulting in a catastrophic defeat for the latter. Although both sides were utterly exhausted after the titanic clash, Zhao, unlike Qin, could not recover after the event.
In about 50 years Qin superiority was secure, thanks to its powerful military and, in part, constant feuding between the other states.
The Warring States Period saw the introduction of many new innovations to the art of warfare in China, such as the use of iron and cavalry.
The various states fielded massive armies of infantry, cavalry and chariots. Complex logistical systems maintained by efficient government bureaucracy, was needed to supply, train, and control such large forces. The size of the armies ranged from tens of thousands to several hundred thousand men.
Iron became more widespread and began to replace bronze. Most armour and weapons of this period were made from iron.
The first official native Chinese cavalry unit was formed in 307 BC by King Wuling of Zhao. But the war chariot still retained its prestige and importance, despite the tactical superiority of cavalry.
Crossbow was the preferred long range weapon of this period due to many reasons. The crossbow could be mass-produced easily, and mass training of crossbowmen was possible. These qualities made it a powerful weapon against the enemy.
Infantrymen deployed a varieties of weapons, but the most popular was the dagger-axe. The dagger-axe came in various length from 9–18 ft, the weapon comprising a thrusting spear with a slashing blade appended to it.
In 225 BC, Qin conquers Wei. The Qin army led a direct invasion into the state of Wei by besieging its capital Kaifeng (大梁) but soon the Qin army realized that the city walls were too tough to break into and so they devised a new strategy in which they utilized the power of a local river which was linked to the Yellow River. The river was then used to flood the city's walls, causing massive devastation to the city. Upon realizing the situation, King Jia of Wei (王假) hurriedly came out of the city and surrendered its city to the Qin army in order to avoid further bloodshed of his people.
In 223 BC, Qin invades Chu. The King of Qin, Ying Zheng, decided to first defeat the strongest state, Chu. However, the first invasion was doomed to utter disaster when northern style Qin troops were defeated by 500,000 Chu troops in the unfamiliar territory of Huaiyang, modern-day northern Jiangsu and Anhui provinces. The Qin general was Li Xing, who was inexperienced.
In 224 BC., the famed conqueror of the state of Zhao, Wang Jian, was recalled to lead a second invasion with 600,000 men. Chu's morale was greatly increased after their success in defeating the seemingly invincible army of Qin the year before. The Chu forces were content to sit back and defend and believed it was Qin's intention to besiege Chu. However, Wang Jian tricked the Chu army by appearing to be idle in his fortifications whilst secretly training his troops to fight in Chu territory. After a year, Chu decided to disband due to inaction. Wang Jian invaded at the best moment with full force to overrun Huaiyang and the remaining Chu forces. Chu lost the initiative and could only sustain local guerrilla-style resistance until it too was fully conquered in 223 BCE. During their peak sizes, both armies of Chu and Qin combined numbered over 1,000,000 troops, more than the massive battle of Changping between Qin and Zhao 35 years before but which the Qin was able to conquer the state of Chu at last.
In 222 BC, Qin conquers Yan and Zhao. After the conquest of Zhao the Qin army then turned its attention towards the state of Yan. Realizing the danger & gravity of this situation, Yan Prince Dan had sent an assassin Jing Ke to kill the Qin emperor but this failure only helped to fuel the rage & determination of Qin Shi Huang and he increased the number of troops to conquer the state of Yan.
In 221 BC, Qin conquers Qi. Qi previously did not contribute or helped other states when Qin was conquering the other states and as soon as Qin was aiming for its final target the Qi quickly made the same decision as the Han did some nine years earlier and surrendered all its cites to Qin, completing the unification of China, and ushering in the Qin Dynasty.