China, a History

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 ascend 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), 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), 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) where Wei was decisively defeated. The event spawned the idiom "圍魏救趙", 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).

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 states became the two dominant states in China.