During the first years of the Zhou Dynasty, Yan was located near the Yellow River, but after the failed revolt led by the leaders of the Shang Dynasty, the fiefdom was relocated further north in what is now Hebei Province to stop the invasion of the northerly tribes.
The borders of Yan were approximately in a horizontal shape, stretching from the mountains of Shanxi Province to the Liaodong Peninsula. As the most northeastern of all the Chinese states during this time period, it suffered several invasions from Mongolia. The border states of Zhao and Qi were its main enemies. The mountainous border in the west between Zhao and Yan became the area in which their armies often clashed. Despite this, the war between Zhao and Yan usually dragged on into a stalemate, requiring the help of other kingdoms to conclude.
The strongest opposition came from the Qi, one of the strongest states in China. In 314 BC, taking advantage of a succession crisis within Yan, Qi invaded and in a little over several months practically conquered the country. However, due to the misconduct of Qi troops during the conquest of Yan a revolt eventually drove them away and the borders of Yan were restored. Yan's new king, King Zhao of Yan then plotted with the states of Zhao, Qin, Han and Wei for a joint expedition against Qi. Led by the brilliant tactician Yue Yi, it was highly successful and within a year most of Qi's seventy walled cities had fallen, with the exception of Zimu and Lu. However with the death of King Zhao and the expulsion of Yue Yi to Zhao by the new king, King Wei of Yan, General Tian Shan managed to recapture all of the cities from the 5 kingdoms.
Despite the wars, Yan survived through the Warring States period. In 227 BC, with Qin troops on the border after the collapse of Zhao, the Yan Prince Dan sent an assassin named Jing Ke to kill the king of Qin, later First Emperor of Qin, hoping to end the Qin threat. The mission failed, with Jing Ke dying at the hands of the King of Qin in Xianyang.
Surprised and enraged by such a bold act (one that came terribly close to causing his demise), the king of Qin called on Wang Jian to destroy Yan. Crushing the bulk of the Yan army at the frozen Yishui River, Ji fell the following year and the ruler, King Xi, fled to the Liaodong Peninsula.
In 222 BC Liaodong fell as well, and Yan was totally conquered by Qin. Yan was the third last state to fall, and with its destruction the fates of the remaining two kingdoms were sealed.
King Wu Chen of Zhao eventually sent his General Han Guang to conquer Yan for Zhao, but upon his conquest, Han Guang appointed himself King of Yan. Han Guang had sent his general Zang Tu to assist Xiang Yu in the war against Qin, and when Zang Tu returned Han Guang was ordered to become King of Liaodong instead. When Han Guang refused, Zang Tu killed him and declared himself King of both Yan and Liaodong.
Zang Tu submitted Yan to Han during the war between Han and Chu in order to keep his title, but once the war was finished he revolted. Liu Bang sent Fan Kuai and Zhou Bo to put down the rebellion, and they executed Zang Tu.
Lu Wan became the new King of Yan and reigned there for most of Liu Bang's life until he failed to meet a summons to the Imperial Court due to illness. He fled to the Xiongnu to avoid being executed. Yan then came under rule of the Han Dynasty.