This was an extremely important move for Cao Cao following the suggestion from his primary advisor, Xun Yu, commenting that by supporting the authentic emperor, Cao Cao would have the formal legal authority to control the other warlords and force them to comply in order to restore the Han Dynasty.

Xian was persuaded by Cao Cao ( 155 – 220 CE ), then Governor of Yan Province in modern western Shandong and eastern Henan, to move the capital to Xuchang in 196 CE.

In the winter of 220, Cao Pi made his move for the imperial throne, strongly suggesting to Emperor Xian that he should yield the throne.

However, he was afraid to move when Cao Cao's bodyguard, Xu Chu, glared at him.

Tension between Cao Cao and Yuan Shao started to build up since Cao Cao received Emperor Xian from the old capital Luoyang, a move that Yuan Shao had considered but not acted upon, much to his regret.

Before his advisers were able to change his mind, Cao Cao consented, commissioned Liu Bei and Zhu Ling with an army to move south.

Early the next year, Cao Cao came personally to Luoyang to move the emperor to his secured base in Xuchang.

In 254, Sima made a violent move to consolidate power at the expense of Cao Fang.

Since Xu Huang refused to lead the reinforcement to the scene right away, Cao Ren once thought about giving up Fan fortress, but his strategist, Man Chong reminded him that the water level would go down sooner or later and that Sun Quan would attack Guan's rear any time ; thus, Cao Ren told his men that he was willing to defend the city with his own life, and everyone was touched, and agreed to hold out until Xu made his move.

Subsequently, on the death of Tao Qian, Cao Cao was tempted to turn around and move on Xu Province before returning to deal with Lü Bu ; it was Xun Yu who dissuaded him from this, reminding him that Yan Province was his heartland and power base and should be secured first before launching campaigns abroad.

Knowing that Dong Zhao was probably a conduit for Cao Cao, when approached by the former for his support, Xun Yu told Dong that Cao's personal mission was one of restoring the Han Dynasty and would not approve of such a move — thus possibly hinting to Cao that he should abandon the idea.

In 216, the warlord-statesman Cao Cao detained Hucuquan in the city of Ye, and divided his followers in Shanxi into five divisions: left, right, south, north, and centre.

Meanwhile Colonel Charton's group, led by the 3rd Battalion of 3rd REI, left Cao Bang on 1 October ; contrary to orders he took with him his heavy equipment.

Royal Uncle Cao was so overwhelmed by sadness and shame on his brother that he resigned his office and left home.

He did not take any of Cao Cao's gifts with him and left behind a farewell letter.

Frustrated, Guan Yu eventually wrote a farewell letter to Cao Cao and left.

When Cao Cao was leading a campaign against Tao Qian, the governor of Xu Province ( 徐州 ; covering present-day northern Jiangsu ) whom Cao accused of killing his father, Xiahou Dun was left with the responsibility of defending Yan Province.

" Cao laughed and left.

Zhang Fei, who was left behind by Liu to guard Xiapi ( capital of Xu Province ), killed Cao Bao ( chancellor of Xiapi when Tao Qian was still in charge of Xu Province ) after an intense quarrel.

Yuan Shao's attempt to reinforce Liu was repulsed by Yu Jin, whom Cao Cao had left in command of his troops at Yan Ford.

He retreated back to the north and left behind Cao Ren and Xu Huang to guard Jiangling and Yue Jin to defend Xiangyang.

Cao Cao perfunctorily retreated to the north, and left Cao Ren and Xu Huang at Jiangling in Nan Commandery ( 南郡 ), Yue Jin in Xiangyang, and Man Chong at Dangyang.

In one occasion, the enemy commander, Zhou Yu, left the defense of his main camp to his subordinate, Ling Tong, and led most of the troops to rescue another subject, Gan Ning, who was surrounded by Cao Ren's cavalry in a distant castle.

Even Ling Tong was only left with a wee fraction of the army to guard the camp, the numerically superior Xu Huang and Cao Ren were defeated by the former and the enemy camps remained intact.

He left Cao Cao after learning of Liu Bei's whereabouts and rushed to reunite with Liu.

When Guan Yu left Jing Province to attack Cao Cao's forces in the north, Lu Xun pretended to take over Lü Meng's command of the military on Jing Province's eastern front.

After settling the nearby provinces, including a rebellion led by former Yellow Turbans, and internal affairs with the court, Cao Cao turned his attention north to Yuan Shao, who himself had eliminated his northern rival Gongsun Zan that same year.

Yuan Shao, himself of higher nobility than Cao Cao, amassed a large army and camped along the northern bank of the Yellow River.

Overcoming Yuan Shao's superior numbers, Cao Cao decisively defeated him by setting fire to his supplies, and in doing so crippled the northern army.

* Three Kingdoms: The northern part of China is under the control of Cao Cao, Imperial Chancellor and ruler of the Kingdom of Wei.

In winter of that year, the northern warlord Cao Cao led an army of some 830, 000 to conquer south to complete the reunification of China.

Immediately, after Cao Cao withdrew, Sun Quan took over the northern half of Jing Province.

Cao Pi declined, in a fateful choice that most historians believe doomed his empire to ruling only the northern and central China — and this chance would not come again.

Survivors of the Mạc royal family fled to the northern mountains in the province of Cao Bằng and continued to rule there until 1677 when Trịnh Tạc conquered this last Mạc territory.

Through his conquests, Cao unites the Central Plains and northern China under his rule, and the lands he controlled would serve as the foundation for the state of Cao Wei in the future.

Xuchang in central Henan was the power base of Cao Cao, who eventually succeeded in unifying all of northern China under the Kingdom of Wei.

Cao declined this suggestion, in a fateful choice that most historians believe doomed his empire to ruling only the northern and central China ; Such an opportunity would not come again.

It marked the beginning of Cao Cao's gradual reunification of northern China, which made the establishment of the state of Cao Wei possible.

Cao Pi's strategist Liu Ye suggested that Cao Pi decline — and in fact attack Sun Quan on a second front, effectively partitioning Sun's domain with Shu, and then eventually seek to destroy Shu as well.

Cao's strategist Liu Ye ( 劉曄 ) suggested that Cao decline and instead attack Sun on a second front.

The front of the Cao E Temple, facing east, toward the river.

During the first battle of Ruxu, in which Cao Cao personally led 400, 000 men with the intention to crush the 70, 000 men Sun Quan gathered, Xu Sheng served as a captain in the front division for Sun.

Liu then asked Wei in front of the mass how would he serve his new post, wherein Wei confidently replied: " If Cao Cao mustered all his forces and invaded, let me assist my lord to repel the enemies ; if an Assistant-General came with 100, 000 troops, let me engulf them for my Majesty.

In an unusual move, Cao turned his entire formation around, placing the supplies in front.

" Kong Rong wanted to recommend Mi Heng to Cao Cao, but Mi put up a rude and arrogant attitude in front of Cao.

Henceforth, whenever Cao Cao personally led a campaign abroad, Yu would be placed in front as the vanguard commander.

Cao Cao's personal bodyguard Dian Wei died defending the front gate to the camp so that Cao Cao could escape through the back.

The next morning, Yuan placed the commoners, who were hastily armed during the night, in front of his troops and marched into battle with Cao Cao outside the city.

Showing no fear nor resistance, Gao then saw Cao shifting his attention to him, and guards surrounding Gao hustled him in front of Cao.

Three years after Cao defeated Yuan at the Battle of Guandu, Cheng recruited and enlisted several thousand robbers and inhabitants of deep hills around Yanzhou, and led them to rendezvous with Cao in Liyang, where Cao set up as a front line military operation base against Yuan Tan and Yuan Shang.