755 CE: Major Point of Divergence
An Lushan, the engineer of the OTL An Shi Rebellion, is suspected of treason by Yang Guozhong, a Tang official. Yang Guozhong convinces the Tang emperor to have a spy become close to An Lushan. The spy eventually gets information about the planned rebellion, and An Lushan is executed. Although there are scattered small-scale rebellions during times of drought, the An Shi Rebellion never takes place.
755 - 985 CE: Late Tang Dynasty
The Tang Dynasty (唐朝) continues relatively unscathed for more than 200 years after the attempted rebellion. During this time, many technological advances take place, including militarily, as with the invention of gunpowder. Primative guns and bombs develop soon after. Buddhism continues to flourish, while Confucianism and Daoism also make somewhat of a comeback.
985 - 1200 CE: Zheng Dynasty
The abrupt end of the Tang Dynasty would come about through Zheng Huozi (郑火子), an able soldier and Confucian scholar from Henan, who would capture the emperor and start his own dynasty. Stationed in Hebei and witnessing attacks from barbarians, he urged the Tang emperor to take measures to beat back the attacking hordes. He said that the citizens were lazy and used to a good life at the expense of defending the country. The Tang Emperor, however, did not do anything about the situation, as he felt that stability was good and that further excursions were unnecessary. Zheng Huozi and his crew then used this as a pretense to stage a coup and become emperor, jailing the last Tang Emperor for failing the Mandate of Heaven. With Zheng in charge, the Zheng Dynasty (征朝) began its nearly 350 year run.
Secretly, Zheng had not only wanted to conquer the barbarians (consisting mostly of Mongol, Turkic, and Tungusic tribes), but also wanted China to have an outlet into the Western Ocean - that is, the Indian Ocean - both for trading purposes, and also simply for a great show of empire building. Zheng began procuring and training people to be soldiers, including the teaching of barbarian skills such as fighting while horse riding. By 995, Zheng China had by far the largest military in the world and on the tenth year of the Emperor's rule, he started a war of subjugation that would eventually encompass much of Asia.
995-998: Northern Campaigns
The Great Chinese army first swept through the north defeating such groups as the Uyghurs, Kyrgyz, Jurchens, Mongols. In less than 1 year, these gains came to include much of OTL Southwestern Russia. The ethnic groups under Chinese control began to be "civilized" forcefully, with laws against speaking their languages and performing their traditional rituals in public. These barbarian tribes were relocated into towns, and would eventually lose their nomadic spirit, as well as their languages and culture. For example, by the year 1300, the Mongolic languages completely ceased to exist.
999-1015: Western Campaigns
In 999, Chinese troops flooded over the northern boundary of the Pamir Mountains  and swept south to take Ghazna  in the spring of 1000, thus ending the short-lived Ghaznavid Empire (OTL Afghanistan). Soon after their major victory over Ghazna, they pushed farther south and reached the shores of the Indian Ocean, completing their domination of the OTL Afghan region and Persia. By 1003, the Cuman Tribes (Western Turks) were overcome, and the east coast of the Caspian Sea was in the hands of the Chinese. By this time, the Chinese were directly at odds with the Abbasid Caliphate, which was already in a period of decline. Progress halted for a while in Mesopotamia, as the Chinese had to wait for some re-inforcements to come. However, at the emperor's insistence, further recruitment took place and China's army swelled further. Also, breakthroughs using gunpowder bombs took place and were tested in combat use against the Abbasid Caliphate. Emperor Zheng, upon hearing that the Mediterranean was so close, wanted to push on further to gain it In 1012, Baghdad fell and the Abbasid Caliphate was no more. Further major annexations occurred until around 1015, when the conquered territories were consolidated.
After the Major Campaigns
After the military campaigns, the Zheng Dynasty of China signed various peace treaties, including ones with the Byzantine Empire, the Fatimid Caliphate (of Northern Africa), and some Indian entities such as the Solankis, as it had already done with Goryeo (Korea) and Japan before the campaigns. Emperor Zheng Huozi puts ethnic Chinese people in charge of all new territories, also keeping bodyguards and generals ethnically Chinese. However, he allows conquered peoples to climb the ranks, and some former enemies are able to attain certain high positions. The highest of the rulers, during much of the Zheng Dynasty must also send their first-born male children to the capital of China, which had been recently moved to Beijing from Chang'an (or Xi'an). This helped to ensure that no faraway governors would take it upon themselves to declare independence and establish themselves as kings. Zheng Huozi died in 1025, with his son, Zheng Baitong (郑拜僮) taking over. Emperor Baitong was generally a good ruler, although he was prone to get angry when shown disrespect in any way. He was also a perfectionist, and didn't care much how things got done or how much it would cost to get them done, as long as they got done. With the passing away of his father and the reduction in active Chinese troop numbers, some of the subjugated peoples, as well as bordering people lost some fear in the government. This was also due to memories of war fading and a new generation growing up without any memory of war. Although arguably most subjects of the empire thought of themselves as such, there were some groups that rebelled. However, these were easily put down by the still-strong government.
1036-1039: Arab-Egyptian Campaign
In 1036, there was a tremendous attack upon the Zheng Dynasty by Muslim Arabian tribes. The assumed reason was that the border of the Chinese Empire lay just north of Medina, one of the Holiest cities of Islam. The Arabians, angry about the overthrow of the Abassid Caliphate and unwilling to let Godless heathens into their religious cities, even for trade, outright refused the visits of emissaries from China. This also angered the Chinese Emperor, who was used to being shown respect. During the early 1030s, China also apparently received word that the Fatimid Caliphate was giving weapons to the Arab tribes (although there was no conclusive proof that it was the Fatimid government's own doing). However, when in 1036, a massive well-armed force broke through the Chinese Empire's border towards Baghdad, both the Arabians and the Fatimids in Egypt were put in the crosshairs of Chinese fury. The new emperor felt that he needed to prove himself by showing great force towards his opponents, and this was the instance that he desired. The Arabians besieged Baghdad, and the Chinese were in the situation of having to hold on for more than a month until a substantial number of Chinese troops arrived. In the meantime, some regiments made up of conquered peoples (which were by law barred from utilizing some Chinese-exclusive weaponry) had to suffice. Eventually, Baghdad fell to the Arabians because a large part of the Muslim population in Baghdad itself rebelled and wouldn't fight. However, a few weeks later, the well-armed and 500,000 strong Chinese army retook the city and then moved on to wage war with the rest of Arabia. In as little as a year, the whole Arabian peninsula was under Chinese control. At the same time, an offensive against the Fatimid Caliphate commenced, even though there had been a peace treaty signed and the Caliphate never admitted to helping the Arabians. Chinese troops swept into Egypt, subduing the capital of Fustat and claiming the royal palaces at Cairo. The Fatimid rulers escaped to Ifriqiya (or Tunisia), setting up shop with the Zirids. The Chinese pushed towards Kairouan, where the new Fatimid capital was, but never succeeded in taking it. In late 1039, the fighting stopped, with Chinese control over both Arabia and Egypt.
The Muslim Persecution
Partly because of the betrayal of the Muslims in Baghdad, and partly as a show of force, and probably also because the Muslim subjects in general seemed to be the hardest to gain the loyalty of, there began a great persecution. Firstly, both Mecca and Medina, which had shown such contempt for the Chinese by not allowing even one to enter, were burned and beaten completely to the ground. Zheng Baitong ordered that the cities return to the desert so that nobody could have them. All of the sacred artifacts of the cities were desecrated, and the "black stone", a meteoroid remnant in the kaaba, was taken back to the emperor in Beijing. Secondly, after hearing of the desecration of their holy cities, adult male Muslim civilians across the empire were made to state that the Emperor had the "Mandate of Heaven". Those who failed to do so were put to death. This lasted from 1037 until 1047 - a full ten years. Afterwards, things were more relaxed, although Muslims (and non-Chinese in general) were continued to be viewed with suspicion. Because of the desecration of the two most holy cities in Islam, Kairouan (in Fatimid Tunisia) became the most holy city, although Muslims never stopped praying in the direction of the former Mecca.
1053-c.1100: Economic and Cultural Revival
During the war years, which the vast majority of Chinese had been born under, the nation had shown its amazing strength that it had largely gained during the Tang Dynasty and then unleashed during the Zheng Dynasty thus far. However, culture had stagnated and by the end of the war years, China was in debt. The almost forgotten Tang life had been an easy one for most, with a quality of life much higher than in most other places in the world those days. But more and more, young men had not been able to continue in their father's businesses, whether it was growing food or inventing new devices of all sorts. Instead, they were being sent halfway around the known world and dying fighting enemies that hadn't even existed in their parents' minds. Many Chinese didn't want any more fighting. What they had conquered was good enough. In fact, China proper was even good enough. This was the thinking during the war and up to the middle of the century, when the third Zheng emperor took the throne.
In 1053, Zheng Feiling (郑肥令) took power. During his rule, China's relations with neighboring countries and internal minority groups improved. Especially concerning trade, China came back to life. With less chaos in the empire, the Silk Road resumed. And now, because of its conquests, China had complete sovereignty over the whole land route, excepting the Indian sub-branch. This proved to be beneficial for trade because China's standing army (again smaller than during wartime) patrolled the major routes to keep them safe for traders. Before, bandits had been common. With the sea route, the Malay kingdom of Srivijaya (ஸ்ரீ விஜய) prospered. During this period, the Sri Vijayan town of Temasek (டெமஸெக்) (or Sea Town) started to grow rapidly. It was located on an island (Pulau Ujong / புலௌ உஜொங் / புலௌ உஜுங்) at the tip of the Malay peninsula, around which every maritime Silk Road ship going to or from China would have to pass.
Distrust between the Byzantine Empire and the Chinese Empire was palpable, but trade relations trumped it for the most part.
1100-1182: Japan and Sri Vijaya Become Sea Merchants
Throughout much of the 12th century, Japan and Sri Vijaya prosper. In response to the tremendous growth of long-distance maritime trade, Sri Vijaya and Japan start building up great trading and military fleets. China, on the other hand, focuses more on land transport, and foregoes a large blue-water navy for a green- and brown-water (close to shore) navy. As a major land power, and with long-distance sea trade still in its infancy, China does not yet realize the power that navies can be brought to bear. In fact, China encourages the Japanese to act as traders between China, Sri Vijaya, and India. Over the decades, these ships, as well as the distances that they travel, continue to grow. Sri Vijaya is also busy in its attempt to become a major power. One helpful situation is the fact that all sea traffic from India to China has to pass through the Vijaya Strait (ஸெலட் விஜய; OTL Strait of Malacca), and thus through Sri Vijaya's waters. Taking great pains not to become a Chinese vassal state, it stayed on good terms with its larger brother to the north. By the mid-1100s, Japan and Sri Vijaya are rich from trade, while China has maintained its dominance. Thus far, China's perceived might kept others from posing a great threat, but this would change as China was set to implode.
1182-1200: The Fall of the Zheng Dynasty and the Break-up of China
1182 was the beginning of the end of Zheng China. Starting around the mid-1100s, the Chinese emperors became increasingly greedy. The Imperial Household became infamous for its ubiquitous displays of wealth and for its turning a blind eye to the increasing gap between rich and poor in the country. Important posts in the military and trading companies were filled with the friends and family of the emperor, showing that cronyism had overturned the meritocracy of the past. Also in 1182, there was a local famine around Beijing, which many of the people attributed to bad governance. A riot formed in the capital and grew so large that the emperor had to flee, and the imperial palace was taken by the mob. At this point, some prominent army leaders cut allegiance to the emperor and declared that they were now in power. This was the beginning of the Dynasty of Generals. However, a large part of the army, as well as of the populace, were still loyal to the emperor. The emperor moved his court to back to the older capital of Chang'an (Xi'an) and set up a competing government. When the governors of the outer territories heard about the rebellion in China proper, several of them decide to break away. The policy of governors sending their first-born sons to the capital as leverage against declaring independence was still in force, but during the riots, many of them were able to escape the capital. Some joined their governor fathers. Some governors declared independence without their first-born sons present, as by this time, the culture amongst governors had changed to the extent that first-born sons were the expendable ones. By 1184, three regions (North Africa and Arabia, the Kipchaks (along with other Turks), and Persia) had broken away from China, and China was still divided in two. The governors of the Kipchak and Persian regions stated that they would rejoin China once the emperor regained the throne. However, the North Africa and Arabia region declared its independence from China outright. (It is important to note that it wasn't the populace of these regions that declared independence, but rather the Chinese governors who did. Thus, these areas would continue to be under Chinese cultural dominance for decades, until the Chinese upper class started to assimilate into their respective nations while also profoundly altering the previous culture, with the process mostly complete by 1300, when China would again awaken and start to expand again.) At any rate, the end of the Zheng Dynasty came in 1189, when the emperor's troops were defeated by the group that defected from the army, and their control soon encompassed all of old China proper (that is, minus the areas that had declared independence). However, throughout the 13th century, the army defectors and their kin would battle each other, and the break-away states, to reign supreme, and China's role in world affairs would be severely undermined for a century.