Tell the truest history in the simplest words.
The State of Yan, one of the Seven Heroes of the Warring States, had a large-scale successful expansion operation and made great contributions to the development of the Chinese nation. This is the battle achievement of Qin Kai but Donghu taking Liaodong. There are two historical sources:
Qin Kai but Hu
"Yan Youxian took Qin Kai as a hostage to Hu, and Hu believed in it. Returning to attack and break away Dong Hu, Dong Hu was more than a thousand miles, and Jing Ke stabbed the Qin King Qin Wuyang, kai's grandson also. "The Chronicle of History. The Biography of the Xiongnu "Descendants were slightly arrogant, the people of the country left their minds, Yan Nai sent Qin Kai to attack its west, taking more than 2,000 miles of land, to the border of Manban Khan, and Korea was weak" Chronicle of the Three Kingdoms. Qin Kai, a character lying in the History Book, is not well known to the public. But his military talents and great achievements are also recorded in the long scrolls of history.
I think that Qin Kai's merits are comparable to Le Yi for the Yan Kingdom; for the Chinese nation, Le Yi is far inferior. The historical data do not indicate the specific age, which is roughly introduced by the present people, and it belongs to the same time as the Yan Zhaowang raised an army to cut down Qi.
In order to make all-out efforts, King Zhao of Yan entered Donghu with the Guiguan of the Yan state (including Qin Kai) in order to stabilize the rear. By the time Yan Wu became king, Qin Kai, who was well aware of The Unreality of Eastern Hu, returned to China. King Wucheng attacked Eastern Hu in the north with qin Kaitong's army and won a complete victory, while Eastern Hu retreated to the north and fled, and the northern border of the Yan kingdom was greatly expanded, known as "more than a thousand miles" of the expansion of the land. The Yan army also took advantage of the victory to attack Korea in the liaoshui area from the east, seizing a vast area of liaodong, and even extended south of the present-day Yalu River, "until the border of Manban Khan".
Qin Kai was taken into Donghu as a hostage by the powerful Hu people during a raid on Donghu. Perhaps it is the difference in the geographical location of the northern nomads, there is not much grain to feed, and there is no fine clothing in the Central Plains to be comfortable, they just have endless white clouds and cattle and sheep running on the ground. In order to survive, they went south. Relying on their strong physique, harassing the Central Plains, running rampant in the townships, burning and looting, the residents of the border cities of Yandi could only leave their hometowns and leave their hometowns behind them.
Qin Kai walked into Donghu in this context. On a horse selling trip, Qin Kai, who had been planning for a long time, broke away from the team, and it happened that the yanguo's team was passing by. After returning to China, Qin Kai was appointed as a general and began his career as a soldier. At this time, the monarch of the State of Yan was a famous King of Yan Zhao in history.
Qin Kai was a famous general of the Yan state, very rich in combat experience, experienced in the battlefield, a hundred battles and hundreds of victories, and was very familiar with the situation of Eastern Hu, in 283 BC Qin Kai led an army to meet Eastern Hu, the Yan army from west to east, from the Yushui River Basin (in present-day Yanqing) to the Miyun area of Yushui (present-day Baihe), Baoqiu Water (present-day Chaohe) river basin, all the way to cut the pass to seize the pass, Ma stepped on the Pingchuan, although the Eastern Hu army struggled to resist, but could not stop the Yan army's fierce offensive, had to retreat all the way, the Yan army took advantage of the victory to pursue, and successively recovered the lost land.
Under the successive victories, the morale of the Yan army was even stronger, and they chased donghu to the northeast with one drum. The resistance was useless, and it retreated to the upper reaches of the present-day Xiliao River, more than a thousand miles away.
At this time, Qin Kai stood on the northern border of Yan and planned a stabilization strategy. Following the example of the Zhao State, mobilizing the military and the people to repair the barrier, so that the Northern Great Wall of the Yan Kingdom, which is more than 2,000 kilometers long, still exists in the north of today's Jianping, but it is only a section of it, but it is only the erosion of the wind and rain today, and the remnants are dilapidated, but it is also faintly recognizable that Yan has consolidated the new area, and also followed Zhao's deeds, mobilizing the military and civilians to repair the barrier, which is more than 2,000 kilometers long.
Later, Yan successively established the counties of Yuyang, Youbeiping, Liaoxi, and Liaodong in the vast new territory, and Yan surpassed the three kingdoms of Zhao Qiyue in terms of size, second only to Qin and Chu, ranking third among the nations.
Reference: Chronicle of History. Biography of the Xiongnu; Romance of the Three Kingdoms. Dongyi Biography