春秋时期无数次战争使诸侯国的数量大大减少。到战国时期，七个实力最强的诸侯国是齐、楚、燕(yan)、韩、赵、魏(wei)、秦，并被称作“战国七雄”。 战国初期，韩、赵、魏三家结成联盟，打败了齐、秦、楚等大国，成为较强盛的国家。后来这个联盟破裂，齐国、秦国却逐渐兴盛起来。 战国中期，魏国军队攻打赵国，赵国请齐国帮助退兵。魏国内部空虚，大军事家孙膑(b1n)带领齐国的军队直接去打魏国的首都。魏国军队本已攻破赵国首都，听见自己的国家情况危急，便急忙从赵国撤军去救魏国，刚走到半路，就遇上了埋伏的齐国军队，齐国军队堵住魏国军队，打了个大胜仗。这就是中国历史上著名的战例——“围魏救赵”。 两年后魏国进攻韩国，齐国的军队在孙膑的指挥下围魏救韩。齐军假装后退。第一天撤出后营地留下的炉灶足够做10万人的饭；第二天留下的炉灶只够做5万人的饭；第三天留下的炉灶减少到只够做3万人的饭。魏军从炉灶的数量推测，以为齐军大量逃亡，于是挑选了精锐的士兵，追赶齐军，一直追到马陵(今河南省境内)，结果被埋伏在这里的齐军彻底打败。这就是著名的“马陵之战”。两次战役后齐国取代了魏国称霸中原。 战国后期，秦国越来越强盛，其它6个国家都不能单独抵抗秦国，于是就想联合起来，共同抵抗秦国。秦国为了打败其余的六国，挑拨六国之间的关系，促使他们都和秦国亲近。各国为了自身的利益，一到关键时刻常常不能齐心合力，结果给了秦国机会。秦国前后征服了其它国家，并灭了周王室，统一了中国。
The Seven Powers of the Warring States Period
By the time of the Warring States Period (475 - 221 BC), only seven vassal states remained, the rest having been absorbed by Qi, Chu, Yan, Han, Zhao, Wei and Qin. These seven states were called the "Seven powers of the Warring States Period". In the early Warring States Period, Han, Zhao and Wei formed an alliance, and defeated Qi, Qin and Chu, separately. Later the alliance broke up, while Qi and Qin gradually gained in strength. In the mid-Warring States Period, the State of Wei attacked Zhao. Zhao asked the State of Qi for help. The great military strategist Sun Bin led the Qi army against the Wei capital. Alarmed at the threat to their own lightly-defended state, the Wei troops, who had already occupied the Zhao capital, withdrew, and Zhao was saved. On their way back to Wei, the Wei forces were ambushed by the Qi army, and were crushingly defeated. This was a famous battle in Chinese history, and gave rise to the saying "besieging Wei and saving Zhao". Two years later, Wei launched an attack against the State of Han. The Qi army, again under the command of Sun Bin, besieged Wei and saved Han. Then the Qi army pretended to retreat. On the first day they left behind enough camp fire sites to cook food for 100,000 soldiers, the second day enough for 50,000 soldiers, and the third day only enough for 30,000 soldiers. The Wei commander speculated that the Qi soldiers were deserting in great numbers. When the Wei forces caught up with a small force of the Qi army at Maling (in today's Henan Province), they were ambushed and put to flight by the full strength of the Qi troops. Qi later replaced Wei as the hegemon of the Central Plains. In the late Warring States Period, Qin became stronger and stronger. The other six states allied against the growing power in the west, but Qin cleverly sowed discord among them, and they could never form a united front against it. Qin vanquished the other states one by one, abolished the Zhou ruling house, and united China under the Qin Dynasty.