Question: What was Cao's first tactical mistake and what were the consequences?
About the article "Battle of Red Cliffs", section "Analysis".

Candidate passages:
A combination of Cao Cao's strategic errors and the effectiveness of Huang Gai's ruse had resulted in the allied victory at the Battle of Red Cliffs.
Zhou Yu had previously observed that Cao Cao's generals and soldiers comprised mostly cavalry and infantry, and few had any experience in naval warfare.
Cao Cao also had little support among the people of Jing Province, and thus lacked a secure forward base of operations .
Despite the strategic acumen Cao Cao had displayed in earlier campaigns and battles, in this case he had simply assumed that numerical superiority would eventually defeat the Sun and Liu navy.
Cao's first tactical mistake was converting his massive army of infantry and cavalry into a marine corps and navy: with only a few days of drills before the battle, Cao Cao's troops were ravaged by sea-sickness and lack of experience on water.
Tropical diseases, to which the southerners had long been immune, also plagued the soldiers of the north with the debilitating effects of sickness rampant in Cao Cao's camps.
Although numerous, Cao Cao's men were already exhausted by the unfamiliar environment and the extended southern campaign, as Zhuge Liang observed: "Even a powerful arrow at the end of its flight cannot penetrate a silk cloth" (Military Documents 1979:193).
The uncharacteristically poor preparation and miscalculations displayed by Cao Cao during this campaign may have been partly due to the recent death of his strategist and advisor Guo Jia.
Cao Cao himself had commented: "Had Guo Jia been with us, I would never have got into such trouble" .
Another key advisor, Jia Xu, had recommended after the surrender of Liu Cong that the overtaxed armies be given time to rest and replenish before engaging the armies of Sun Quan and Liu Bei, but Cao Cao disregarded the advice .
Cao Cao's own thoughts regarding his failure at Red Cliffs suggest that he held his own actions and misfortunes responsible for the defeat, rather than the strategies utilised by his enemy during the battle: "... it was only because of the sickness that I burnt my ships and retreated.
It is out of all reason for Zhou Yu to take the credit for himself."
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The first incident that illustrates the righteousness of Chen Gong comes in Chapter 4, where Cao Cao was fleeing from the capital Luoyang after a foiled assassination attempt on Dong Zhuo.
At Zhongmu County (中牟縣), where Chen Gong was the magistrate, Cao Cao was captured.
When Chen Gong interrogated the fugitive, he was so impressed with Cao Cao's loyalty to the emperor that he decided to abandon his official post and join Cao Cao, who planned to return to his home in Chenliu (陳留; around present-day Kaifeng, Henan) to raise an army against Dong Zhuo.
Along the journey, they passed by the house of Lü Boshe, a sworn brother of Cao Cao's father.
There, they killed Lü Boshe's family by mistake, while Cao Cao personally murdered Lü in cold blood later.
(See the article on Lü Boshe for details.)
Chen Gong was shocked by what he witnessed.
That night, as Cao Cao slept, Chen Gong considered killing him, but thought it unrighteous to do so.
He instead left Cao Cao and travelled to his own hometown of in Dong commandery (東郡; near present-day Puyang, Henan). 
By autumn in the eighth lunar month, as Cao Cao's army reached the valley of Daling River (大凌河), Tadun and his allies realized what was happening and hastily withdrew from their prepared positions and gathered to face Cao Cao to the north.
With tens of thousands of men gathered, Tadun, along with Yuan Shang, Yuan Xi, and the two Wuhuan chanyu Louban and Wuyan (烏延), met Cao Cao's army at White Wolf Mountain (白狼山; near present-day Lingyuan, Liaoning).
The encounter was sudden for both parties.
Faced with superior numbers and the baggage left in the rear, Cao Cao's lightly armoured men became afraid.
The Wuhuan, on the other hand, were evidently unprepared for battle as they were not in proper formations, nor did they attempt to take the initiative by harassing Cao Cao's march.
Undaunted, Cao Cao climbed a slope to observe the enemy's formations.
He saw that the Wuhuan were unordered, and immediately unleashed his soldiers to exploit this weakness.
With general Zhang Liao leading the offensive, the light force swiftly defeated the Wuhuan cavalry, and Cao Chun's brigade captured Tadun.
Within a short time, Tadun and many of his men were killed and the battle was over.
Over 200,000 Chinese settlers and Wuhuan tribesmen surrendered to Cao Cao. 
Politico.com declared Cao's victory one of America's"Top 10 Political Upsets" of 2008.
Cao became the first Vietnamese-American elected to Congress.
Cao's win made the 2nd District by far the most Democratic district in the nation to be represented by a Republican; the district has a Cook Partisan Voting Index of D+28.
Obama carried the district with a staggering 74 percent of the vote, his 35th-best performance in the country and his fifth best in a Southern district.
Cao's victory over a tainted incumbent became a cause for celebration among many in Louisiana.
Wrote Jeff Crouere in his column "Ringside Politics", "The victory strikes a major blow against the reputation of Louisiana as a corrupt state".
House GOP members were particularly vocal in their glee over Cao's defeat of the Democratic incumbent.
Among many other statements, House minority leader John Boehner asserted Cao's win was "a symbol of our future" in a memorandum with "The Future Is Cao" as its subject line. 
In July, Cao Cao left the capital to lead his troops against Ma Chao, while leaving his son Cao Pi to defend his headquarters in Ye City.
In August, his troops arrived at Tong Pass where the standoff between his forces and the Guanxi forces was taking place.
As the standoff dragged on, more and more Guanxi reinforcements came to Tong Pass, but Cao Cao seemed gleeful at every instance of enemy arrival.
When asked by his officers why he was so happy when the enemy was gaining numbers, he replied "The road to Guanzhong is long, and if the barbarians defended themselves along the treacherous terrain, we cannot conquer them in one or two years.
But now that they all assembled here in this uneasy alliance, it will be much easier to eliminate them.
That is why I am happy.
"Cao Cao gave the Guanxi forces an impression that a frontal assault was imminent, but had Xu Huang and Zhu Ling covertly travelled north.
The two men had slithered cross the Yellow River via Puban Ford (浦阪津) to the west with 4,000 men, and pitchd camp there, circumventing Tong Pass.
A month later, Cao Cao's main force followed, while Cao Cao and Xu Chu guarded the rear.
When Ma Chao got wind of Cao Cao's maneuver, he led roughly 10,000 men to give chase.
Arrows poured down on the rearguard, but Cao Cao was in no hurry.
Seeing that the situation became dire, Xu Chu helped Cao Cao onto a boat, but the ferryman was shot dead.
Xu Chu then used a saddle to shield arrows with his left hand, and paddled the boat with his right.
Ma Chao's men kept on firing arrows on Cao Cao's boat even though it had sailed for miles.
It was then Ding Fei (丁斐), a general under Cao Cao, gave the command to release the livestock.
Seeing this, the pursuing army, being mostly herders, gave up on the chase and went for the horses and oxen instead.
It was through these efforts that Cao Cao safely crossed the river.
Cao Cao's force then regrouped with Xu Huang's, and marched south along the river.
The Guanxi armies then accordingly positioned themselves against attack from the north.
Then, Cao Cao sent out some decoy troops to distract enemy defense while setting up a pontoon bridge crossing the Wei River that would allow his forces to complete the circumvention of Tong Pass.
At night, a portion of Cao Cao's forces crossed the river and tried to set camp; however, the soil was too sandy to be used for building fortification, and Ma Chao's cavalry soon chased away the builders.
Eventually, on the advice of Lou Gui, Cao Cao had his men pour water on piled-up sand.
The mixture froze in the cold night and became solid, and thus a bridgehead was established south of the Wei River.
The icey fortress was shortly attacked by Ma Chao, but the attackers were repelled by Cao Cao's ambushes.
As the battle dragged on, Ma Chao attempted a ceasefire and requested the lands west of the Wei River, but Cao Cao rejected.
Ma Chao would try to entice Cao Cao's men to attack his newly established camp, but Cao Cao did not bite the bait.
In an attempt to negotiate, Cao Cao, Han Sui, and Ma Chao came together bringing no one but their close guards.
Ma Chao had hoped that, with his strength, he could capture Cao Cao and force him to agree to their terms, but he had heard of the prowess of Cao Cao's bodyguard, so he asked, "Is the Tiger Marquis with you today?"
Cao Cao pointed at Xu Chu, who glared at Ma Chao, and Ma dared not make a move.
To avoid attrition, the generals of the Guanxi armies agreed to cede territories and send their sons to Cao Cao as hostages in exchange for peace.
Cao Cao's strategist Jia Xu suggested that he could pretend to accept the terms, and then turn the allied forces against each other.
Cao Cao agreed, and arranged for an armistice.
Han Sui was sent by the Guanxi armies as the representative.
He was once a friend of Cao Cao, and when they met, they did not talk about military affairs but instead recollected their youths in the capital, occasionally clapping their hands and laughing amiably.
When the meeting was over, Ma Chao demanded to know what Cao Cao said, but Han Sui responded that it was nothing much.
Ma Chao became suspicious of Han Sui from there on.
A few days later, Cao Cao sent Han Sui a letter with certain words smudged out as if Han did it himself.
Ma Chao saw this letter and thought Han Sui was collaborating with Cao Cao, and did not trust Han any more.
To capitalize on this suspicion, Cao Cao set the time for a final clash between the two forces.
First, he challenged the allied forces with lightly armoured soldiers, then surrounding the allied forces with heavy cavalry in both flanks.
The allies were routed and several commanders including Cheng Yi and Li Kan were killed in battle.
Han Sui and Ma Chao fled to Liang Province and Yang Qiu to Anding (present-day Anding District, Gansu).
Cao Cao emerged victorious.