During the Warring States (403-221 BC), there was an invasion by Qin Kai of Yan Principality (under King Zhao) in 311 BC, which caused Ko-Choson a loss of 2000-li territory (Yan State have take Korean territories on the west side of Liao River). Qin-kai, after returning from Donghu as a hostage, would attack Donghu or the Eastern Hu barbarians and drive them away for 1000 li distance (Yan state reached Yalu). Yan built Great Wall and set up Shanggu, Yuyang, You-beiping, Liaoxi and Liaodong prefectures. (Qin-kai was said to be ancestor of the lad called Qin Wuyang who accompanied Jing Ke on the journey to assassinating Qin Emperor Shihuangdi.) Today's Koreans called their peninsula via a term of "Beautiful 3000 Li Territory", and a comparative unit of measure could be used for interpretating the ancient "li" measure.
10 三國志魏書東夷傳韓傳魏略曰昔箕子之後朝鮮候見周衰[BC 403?] 燕自尊爲王[323 BC] 欲東略之朝鮮候亦自稱爲王欲興兵逆擊燕以尊周室 燕乃遣將秦開攻其西方[BC 311-297] 到遼東時朝鮮王否立 否死其子準立二十餘年而陳項起[BC 209-8] 天下亂燕齊趙民愁苦稍稍亡往準 朝鮮與燕界於浿水史記卷第一百十匈奴列傳第五十燕有賢將秦開 襲破走東胡東胡卻千餘里 燕亦築長城自造陽至襄平 置上谷漁陽右北平遼西遼東郡而拒胡
The Zhou court (1122 or 1027-256 BC) fell into complete decay and the Warring States period began in 403 BC. According to the Wei-Lüe (quoted in the Three Han section of Dongyi-zhuan), when the Zhou became weak, the ruler of Yan assumed the title of king [in 323 BC]; then the "Lord of Chosun, a scion of Ji-zi" also declared himself king; and these two states were on the brink of fighting each other.The armed conflicts between Chosun and Yan at last occurred c. 300 BC: the Yan dispatched a general named Qin Kai (who was active during 311-297 BC) to invade Chosun. The Xiong-nu section of Shi-ji notes that the Yan greatly expanded its territory, established five provinces, and constructed a Long Wall from Zao-yang to Xiang-ping.10
In the year 284 B.C., Qin Kai, a senior general of Yan State, led troops up and on an eastern expedition. They defeated Donghu/Old Choson and arrived at Liaohe River valley. Afterwards they built a great wall from Zaoyang (now in Hebei Province) to Xiangping (now called Liaoyang). So, Shanggu, Yuyang, Right Beiping, Liaoxi, Liaodong prefectures were founded to resist Donghu. Xiangping, as the capital of the prefecture, marked the beginning of its administrative system.
The conflicts between Old Chosun and Old Yan that were formally recorded in the Chinese dynastic chronicles suggest a fairly intimate relationship (in the form of incessant warfare, as usual between any good neighbors) having been maintained between the Mongolic Xianbei and Tungusic Yemaek people. According to Barnes (1993: 152), the Yan kingdom was the weakest of the seven major Late Zhou feudal states.
The state of Yan, created at the very beginning of the Western Zhou as a fief of an important Zhou lineage and which somehow remained quite obscure for most of the Chungiu period, without active participation of struggles among the Zhou states in the Central Plain, now, probably can be discerned . The Yan was first highly localized by distinctive local conditions until it was reached by the Zhou states again during the Zhanguo period as a result of Jin expansion beyond the Zhongyuan.
Subsequently, Yan also managed to expand. Too little information is available to verify the rather ambiguous account that Yan's expansion reached the border of the Korean peninsula. Nevertheless, the presence of Yan materials in the Liao River valley testifies that the region to its northeast would be one area for Yan to expand into . Then, a rather casual mentioning that a Yan general Qin Kai defeated Donghu tribes and Yan therefore gained a thousand li of new territory . The Donghu who were regarded people of the Upper Xiajiatian culture did not seem to be related to the Shangrong. Were they the enemies in the north who built the Yingqin river defense lines of stone forts? We do not know. This event seemed to have occurred in the late Zhanguo period . Decline of the Donghu gave the Xiangnu an opportunity to rise, and that eventually led to its total domination of the entire steppe-land for at least three centuries, a phenomenon that would significantly have impact upon future changes in the northern Eurasian continent .
From 300 BC (12 years after the Zhao king of Yan kingdom got the power) when the Yan Kingdom dispatched General Qin kai to station troops here for border defence and the general founded Hou City till now, Shenyang
By the early third century BC, while China was still deeply immersed in the Warring States Period, the Korean kingdom of Old Choson armed itself with the latest in metal weaponry and shed its status as a weak confederation of small tribal states. Under the leadership of Ki Pu, the Marquis of Chaoxian, a man with ancestral links to the former Chinese Shang dynasty, Old Choson developed a formidable military presence and soon became an independent power in East Asia with ambitions of its own.
Ki Pu took note of the decline of China's once powerful Zhou clan and knew that the ambitious ruler of Yen, intent on expanding his own realm eastward by seizing the lands beyond the Liao River, had earlier usurped the title of king. The Marquis of Chaoxian gave himself the ancient Chinese title wang, or king, to match his stature. He wanted to gather an army to oppose the powerful State of Yen and support the House of Zhou. Before that happened however, China's Prince Li went to Ki Pu and convinced him to abandon such a plan. Instead of preparing for war, Ki Pu sent Prince Li back to China to persuade the Yen ruler to call off his attack. Prince Li successfully convinced the Yen king not to move eastward and removed the threat of a confrontation, but only for a time.
Ki Pu's descendants grew to become a cruel and arrogant lot. Years later, they began making their own plans to expand Old Choson's influence eastward into the region beyond the Liao River. Before they could act however, a Yen army under the command of General Qin Gai struck the first blow. General Qin's army crossed the Liao River and rapidly fanned out across the flat plains of the Liaodong Peninsula. Before they stopped, Chinese troops seized enough territory in Old Choson to extend China's frontier border over six hundred fifty miles, all the way to Man-p'an-han. In the aftermath of the invasion, Yen established a military district in the annexed territory to insulate China from the threat of further incursions by Old Choson. Under the control of little more than a vague form of overlordship, the Liaodong region became the conduit through which Chinese influences entered northern Korea along the valleys of the Yalu, Ch'ongch'on and T'aedong rivers. The comings and goings of thousands of Chinese officials, merchants, military men, and refugees brought a continuous penetration of Chinese political, economic, and military power to the Chinese occupied lands of the Liao River region.
The bloody defeat of Old Choson at the hands of Yen left a deep impression on the ancient kingdom. Suspicious of Chinese motives, Ki Pu and Old Choson's leadership feared a sudden invasion by the powerful Qin army. To avoid the terrible consequences of such an attack, Ki Pu offered to surrender his kingdom, but refused to travel to the Qin court in Xianyang to do so in person. Ki Pu died shortly afterward, leaving the reigns of leadership to his son, Ki Chun. An invasion of sorts did occur, but it did not come from the Qin army. Tired of the constant political turmoil in Qin and the occupied Liaodong Peninsula, thousands of Chinese refugees fled the embattled areas of north China. The refugees, unwilling to submit to the rule of Chinese military authorities, moved further eastward into Old Choson and settled the western part of Ki Chun's domain. The increased immigration of Chinese led to a rise in the influence of Chinese culture in Old Choson, which entered a period of gradual decline marked by continuous political upheaval.