Alrighty then. I'll start with the Sogdians and Hepthalities inside the Gokturk's realm, and then move on to China, Champa and Korea for PoD changes. And BTW, please be very careful speaking in the chat threads. You might get banned for having a different opinion there these days...
An Analysis on Changes to East Asian History
The Sogdians: When the Hephthalite empire was partitioned by the Sasanians and Turks in 560, Sogdiana passed under the control of the Turks and remained so for a century and a half, for some of the time nominally, but in general the control was fairly direct when it was wielded from Semirechye, where the Western Turk khagans (ḵāqān) and their successors On Ok (lit. Ten Arrows) and Türgesh were settled. Tang China, after defeating the first Turk empire in the middle of the seventh century, also claimed suzerainty over Sogdiana. While it was able to take control over Semiryechye, its armies never reached beyond Tashkent in the south. Thereupon there arose a real Sogdo‑Turkic fusion especially on the elite level, brought about by means of intermarriage, mutual adoption of each other’s customs, hybrid iconography, etc. What we are able to observe in the sixth and seventh centuries at least is the creation of a mid civilization, at any rate among the ruling classes. The Sogdian contributions to the Turkic empire were significant. First and foremost is incontestably the writing. In fact, the Sogdian alphabet gradually adapted to Turkic phonology, was used throughout Turkic and then Uyghur history to write Turkic texts. To this day, the Mongol and Manchu alphabets are distant descendants of the Sogdian alphabet. Moreover, the earliest texts of the Turkic empire were written in Sogdian, beginning in the last quarter of the sixth century, such as the inscription from Bugut, the oldest known one. The role of the Sogdians in the Turkic empire was not restricted to the heights of the state. The Sogdians were numerous in the eastern Turkic empire, which was centered in Mongolia. They then expanded into all the major towns of eastern Asia. Sogdian culture is poorly known. The only major corpus of Sogdian texts discovered in Sogdiana, those from Mount Mugh, are not literary. The sole literary text we have is a fragment of the legend of Rostam in Sogdian, found in China. But the iconography is incomparably richer. At Penjikent, a very large number of wall paintings have been found, which are supplemented by discoveries at Varaḵša, Samarkand, and Šahrestān. Three genres are known: divine, with very elaborate representations of the many Sogdian gods, which borrow many features from the Indian iconographic tradition; heroic, with cycles of epic combat, including Rostam but also other heroes of whom all knowledge is lost; and lastly fables, with images from the Panchatantra. There was also a political painting. Sogdian silverwork fills out this rich iconography.
So there are going to be several differences from OTL here. First off, The Gokturk Khaganate has been re-united under Tardu, and as you put it, poised to continue it's dominance in Central Asia for the next 150 years or so. Without continuous wars, the Sogdian Trade would flourish even better and reach further than OTL, and so would it's people as a result. Second, there'd be more time for not just cultural assimilation of Turkic ideals and culture, but also for Sogdian culture to influence the Turks, if not cultural fusion taking place between the two distinct cultures. Third, if the Sogdians remain favorable to the Khagan, Buddhism (and possibly Manicheaism) could become well tolerated by the ruling classes, and perhaps trigger ecclastical reforms for Nestorian Christianity through Buddhist influences (I think). After all, Although the Buddha preached that "the path to the supreme goal of the holy life is made known only in his own teaching", according to Bhikkhu Boddhi, Buddhists have nevertheless shown significant tolerance for other religions: "Buddhist tolerance springs from the recognition that the dispositions and spiritual needs of human beings are too vastly diverse to be encompassed by any single teaching, and thus that these needs will naturally find expression in a wide variety of religious forms." Multiculturalism and religious cosmopolitanism will also be major factors for such reformations.
The Hepthalites: Despite the fact that they have been relatively defeated and vassalized by the Gokturks, the Hepthalites have actually been placed into an overall better position. You see, now that these fractured, battered states now swear fealty and pay tribute to the Khagan, they are now given all the benefits of open trade with the Gokturks and Sogdians, a possible tolerance of Buddhism (and Nestorian patronage), and most importantly, they will be protected from any kind of attack or invasion by the Hindu States or by Sassanid Persia. If any nation were to attack them, they would also have to deal with the full might of the Gokturks. Given time, the Hepthalites may be able to increase their autonomy under sucessive Khagans, maintain their culture, obtain governmental positions or favors, reorganize their states and finally one day break off from the Khaganate once it collapses, allowing them to once again carve out a great Empire in Bactria once more...
The Tibetans: As the Gokturk Empire is unified and thus a much bigger threat, that along with the consequently different foreign policies of Sui China will greatly alter the foundation and course of the Tibetan Empire...
The Chinese: The Sui Dynasty (581–618 AD) was IOTL a short-lived Imperial Chinese dynasty. Preceded by the Southern and Northern Dynasties, it unified China for the first time after over a century of north-south division. It was followed by the Tang Dynasty. Founded by Emperor Wen of Sui, the Sui Dynasty capital was at Chang'an (which was renamed Daxing). His reign saw the reunification of Southern and Northern China and the construction of the Grand Canal. Emperors Wen and Yang undertook various reforms including the Equal-field system, which was initiated to reduce the rich-poor social gap that resulted in enhanced agricultural productivity, as well as government centralisation and reforms, creating a new model of governance after centuries of division. The Three Departments and Six Ministries system was officially instituted, coinage was standardized and re-unified, defense was improved and the Great Wall expanded. Buddhism was also spread and encouraged throughout the empire, uniting the varied peoples and cultures of China. This dynasty has often been compared to the earlier Qin Dynasty in tenor and in the ruthlessness of its accomplishments. The Sui dynasty's early demise was attributed to the government's tyrannical demands on the people, who bore the crushing burden of taxes and compulsory labor. These resources were overstrained by the completion of the Grand Canal, a monumental engineering feat, and in the undertaking of other construction projects, including the reconstruction of the Great Wall. Weakened by costly and disastrous military campaigns against Goguryeo (in modern day Korea) which ended with the defeat of Sui in the early seventh century, the dynasty disintegrated through a combination of popular revolts, disloyalty, and assassination.
From that basic information, as well as from more on Emperor Wen, we can decipher a possible different outcome due to Tardu's unification of Gokturkey. Instead of facing two separate warring states amongst the Turks, they are united under a strong Nestorian Khagan, Ashina Tardu. This increased threatening prescence amongst China's norther borders would surely concern many if not all the officials and courtesans in the aristocracy, not to mention the Emperor himself and possibly many a commoner. Thusly, if Emperor Wen is able to convince his people that the repair of the Great Wall of China, as well as the building of a Great Canal, is for the portection of the Empire against such Turkic barbarians (Not to mention the Khitai and Gorguryeo too), he'll gain much more support and less unrest for his ambitious building projects. China's foreign policy would also be more cautious; The extensive campaigns against reconquering Dai Viet and invading Champa would probably be called off (or never manifested), any wars fought against Goguryeo (which destroyed the dynasty in the long run OTL) would be mainly defensive (perhaps with a truce asking Goguryeo to attack the Khitai or Baekje/Silla instead, thus cancelling any allusions of alliance with those Southern Korean Kingdoms!). If Sui China can protect itself from the Gokturks, not overextend itself politically, territorially or economically, and reach a truce with Goguryeo (perhaps), then it can possibly last almost as long as the Tang did IOTL.
The Vietnamese and Champans: As a result of different Chinese policies, neither Dai Viet or Champa would be invaded, ravaged and vassalized. Perhaps they could expand into Funan...
The Goguryeo: Any wars China wages upon Goguryeo (which destroyed the dynasty in the long run OTL) would be mainly defensive (perhaps with a truce asking Goguryeo to attack the Khitai or Baekje/Silla instead, thus cancelling any allusions of alliance with those Southern Korean Kingdoms. Without such aid, perhaps Silla and Baekje could be finally conquered by Goguryeo, unifying the Korean Peninsula. Expansion into the Mohe and Khitai tribes is also possible...
An Analysis on Changes to East Asian History
The Sogdians: When the Hephthalite empire was partitioned by the Sasanians and Turks in 560, Sogdiana passed under the control of the Turks and remained so for a century and a half, for some of the time nominally, but in general the control was fairly direct when it was wielded from Semirechye, where the Western Turk khagans (ḵāqān) and their successors On Ok (lit. Ten Arrows) and Türgesh were settled. Tang China, after defeating the first Turk empire in the middle of the seventh century, also claimed suzerainty over Sogdiana. While it was able to take control over Semiryechye, its armies never reached beyond Tashkent in the south. Thereupon there arose a real Sogdo‑Turkic fusion especially on the elite level, brought about by means of intermarriage, mutual adoption of each other’s customs, hybrid iconography, etc. What we are able to observe in the sixth and seventh centuries at least is the creation of a mid civilization, at any rate among the ruling classes. The Sogdian contributions to the Turkic empire were significant. First and foremost is incontestably the writing. In fact, the Sogdian alphabet gradually adapted to Turkic phonology, was used throughout Turkic and then Uyghur history to write Turkic texts. To this day, the Mongol and Manchu alphabets are distant descendants of the Sogdian alphabet. Moreover, the earliest texts of the Turkic empire were written in Sogdian, beginning in the last quarter of the sixth century, such as the inscription from Bugut, the oldest known one. The role of the Sogdians in the Turkic empire was not restricted to the heights of the state. The Sogdians were numerous in the eastern Turkic empire, which was centered in Mongolia. They then expanded into all the major towns of eastern Asia. Sogdian culture is poorly known. The only major corpus of Sogdian texts discovered in Sogdiana, those from Mount Mugh, are not literary. The sole literary text we have is a fragment of the legend of Rostam in Sogdian, found in China. But the iconography is incomparably richer. At Penjikent, a very large number of wall paintings have been found, which are supplemented by discoveries at Varaḵša, Samarkand, and Šahrestān. Three genres are known: divine, with very elaborate representations of the many Sogdian gods, which borrow many features from the Indian iconographic tradition; heroic, with cycles of epic combat, including Rostam but also other heroes of whom all knowledge is lost; and lastly fables, with images from the Panchatantra. There was also a political painting. Sogdian silverwork fills out this rich iconography.
So there are going to be several differences from OTL here. First off, The Gokturk Khaganate has been re-united under Tardu, and as you put it, poised to continue it's dominance in Central Asia for the next 150 years or so. Without continuous wars, the Sogdian Trade would flourish even better and reach further than OTL, and so would it's people as a result. Second, there'd be more time for not just cultural assimilation of Turkic ideals and culture, but also for Sogdian culture to influence the Turks, if not cultural fusion taking place between the two distinct cultures. Third, if the Sogdians remain favorable to the Khagan, Buddhism (and possibly Manicheaism) could become well tolerated by the ruling classes, and perhaps trigger ecclastical reforms for Nestorian Christianity through Buddhist influences (I think). After all, Although the Buddha preached that "the path to the supreme goal of the holy life is made known only in his own teaching", according to Bhikkhu Boddhi, Buddhists have nevertheless shown significant tolerance for other religions: "Buddhist tolerance springs from the recognition that the dispositions and spiritual needs of human beings are too vastly diverse to be encompassed by any single teaching, and thus that these needs will naturally find expression in a wide variety of religious forms." Multiculturalism and religious cosmopolitanism will also be major factors for such reformations.
The Hepthalites: Despite the fact that they have been relatively defeated and vassalized by the Gokturks, the Hepthalites have actually been placed into an overall better position. You see, now that these fractured, battered states now swear fealty and pay tribute to the Khagan, they are now given all the benefits of open trade with the Gokturks and Sogdians, a possible tolerance of Buddhism (and Nestorian patronage), and most importantly, they will be protected from any kind of attack or invasion by the Hindu States or by Sassanid Persia. If any nation were to attack them, they would also have to deal with the full might of the Gokturks. Given time, the Hepthalites may be able to increase their autonomy under sucessive Khagans, maintain their culture, obtain governmental positions or favors, reorganize their states and finally one day break off from the Khaganate once it collapses, allowing them to once again carve out a great Empire in Bactria once more...
The Tibetans: As the Gokturk Empire is unified and thus a much bigger threat, that along with the consequently different foreign policies of Sui China will greatly alter the foundation and course of the Tibetan Empire...
The Chinese: The Sui Dynasty (581–618 AD) was IOTL a short-lived Imperial Chinese dynasty. Preceded by the Southern and Northern Dynasties, it unified China for the first time after over a century of north-south division. It was followed by the Tang Dynasty. Founded by Emperor Wen of Sui, the Sui Dynasty capital was at Chang'an (which was renamed Daxing). His reign saw the reunification of Southern and Northern China and the construction of the Grand Canal. Emperors Wen and Yang undertook various reforms including the Equal-field system, which was initiated to reduce the rich-poor social gap that resulted in enhanced agricultural productivity, as well as government centralisation and reforms, creating a new model of governance after centuries of division. The Three Departments and Six Ministries system was officially instituted, coinage was standardized and re-unified, defense was improved and the Great Wall expanded. Buddhism was also spread and encouraged throughout the empire, uniting the varied peoples and cultures of China. This dynasty has often been compared to the earlier Qin Dynasty in tenor and in the ruthlessness of its accomplishments. The Sui dynasty's early demise was attributed to the government's tyrannical demands on the people, who bore the crushing burden of taxes and compulsory labor. These resources were overstrained by the completion of the Grand Canal, a monumental engineering feat, and in the undertaking of other construction projects, including the reconstruction of the Great Wall. Weakened by costly and disastrous military campaigns against Goguryeo (in modern day Korea) which ended with the defeat of Sui in the early seventh century, the dynasty disintegrated through a combination of popular revolts, disloyalty, and assassination.
From that basic information, as well as from more on Emperor Wen, we can decipher a possible different outcome due to Tardu's unification of Gokturkey. Instead of facing two separate warring states amongst the Turks, they are united under a strong Nestorian Khagan, Ashina Tardu. This increased threatening prescence amongst China's norther borders would surely concern many if not all the officials and courtesans in the aristocracy, not to mention the Emperor himself and possibly many a commoner. Thusly, if Emperor Wen is able to convince his people that the repair of the Great Wall of China, as well as the building of a Great Canal, is for the portection of the Empire against such Turkic barbarians (Not to mention the Khitai and Gorguryeo too), he'll gain much more support and less unrest for his ambitious building projects. China's foreign policy would also be more cautious; The extensive campaigns against reconquering Dai Viet and invading Champa would probably be called off (or never manifested), any wars fought against Goguryeo (which destroyed the dynasty in the long run OTL) would be mainly defensive (perhaps with a truce asking Goguryeo to attack the Khitai or Baekje/Silla instead, thus cancelling any allusions of alliance with those Southern Korean Kingdoms!). If Sui China can protect itself from the Gokturks, not overextend itself politically, territorially or economically, and reach a truce with Goguryeo (perhaps), then it can possibly last almost as long as the Tang did IOTL.
The Vietnamese and Champans: As a result of different Chinese policies, neither Dai Viet or Champa would be invaded, ravaged and vassalized. Perhaps they could expand into Funan...
The Goguryeo: Any wars China wages upon Goguryeo (which destroyed the dynasty in the long run OTL) would be mainly defensive (perhaps with a truce asking Goguryeo to attack the Khitai or Baekje/Silla instead, thus cancelling any allusions of alliance with those Southern Korean Kingdoms. Without such aid, perhaps Silla and Baekje could be finally conquered by Goguryeo, unifying the Korean Peninsula. Expansion into the Mohe and Khitai tribes is also possible...
