A live-streamed Chinese language lesson under the sky—the ancients were taken aback.

Yingtian Prefecture.

Zhu Yuanzhang remained silent for a while, and when he spoke again, his tone was more scrutinizing.

"Emperor Taizu of Song was no ordinary man. He rose from a lowly soldier to become the Commander of the Palace Guards and was eventually crowned with the imperial yellow robe. I admire him."

Regardless of how vividly it is recounted in unofficial histories, the fact that he reclaimed military power did indeed force those powerful military governors who had held sway since the late Tang and Five Dynasties period to obediently relinquish their authority and cease causing chaos in the Central Plains.

He handled things well, and the Song Dynasty was able to remain stable for over a hundred years, avoiding the mistakes of the Tang Dynasty. This was all thanks to him.

Zhu Di stood aside, somewhat surprised. He rarely heard his father speak to another emperor in such a tone.

"Emperor Taizu of Song wasn't afraid to deal with the powerful clans; he simply couldn't. The Five Dynasties and Ten Kingdoms period had lasted for so many years, leaving the Central Plains devastated. The people couldn't withstand any more turmoil. If he were to take action against those powerful clans, the country would immediately descend into chaos."

He paused, his voice returning to its cold, hard tone, "But those officials are really no good either. No matter the dynasty, they dare to chew up and swallow every word of the court's rules, humph."

After he finished speaking, he calmed down and continued to explain the scene on the sky.

"After discussing the economy, let's talk about the territory of the Tang Dynasty after the An Lushan Rebellion."

"To put it simply, it can be summed up in two sentences: foreign tribes occupied the northwest, and warlords carved up the Central Plains."

A comparison map of the territory before and after the An Lushan Rebellion appeared on the screen.

Before the An Lushan Rebellion, the Protectorate of the Western Regions of the Tang Dynasty extended all the way to the west of the Pamir Mountains, bordering Persia.

After the An Lushan Rebellion, the western borders of the Tang Dynasty shrank dramatically. The Tibetan Empire occupied the Hexi Corridor and Longyou, and the Western Regions were completely lost, leaving Guanzhong directly exposed to the Tibetan army.

"Let's look at the Northwest. After the An Lushan Rebellion broke out, the court transferred all the elite border troops from Hexi and Longyou to the Central Plains to quell the rebellion. The Northwest defense line was completely empty, and the Tubo took advantage of the situation to gradually erode the western territory of the Tang Dynasty."

The Tibetan Empire successively conquered the Hexi Corridor and Longyou region, severing the connection between Anxi and Beiting Protectorates and the Central Plains.

This was the most devastating territorial loss in the mid-to-late Tang Dynasty. After the An Lushan Rebellion, the Tang Dynasty forever lost control of the Western Regions and the Hexi Corridor.

The traditional overland Silk Road was completely severed.

"The Anxi Protectorate and the Beiting Protectorate became two enclaves, isolated in the Western Regions, with no one to turn to for help."

The garrison of the Anxi Protectorate held out alone for more than forty years, with no news from the Central Plains.

They didn't receive any reinforcements until the very last moment.

She paused for a moment.

"Those white-haired veterans in Anxi never returned to the Central Plains until their deaths. They upheld the last dignity of the Tang Dynasty, but the Tang Dynasty had long forgotten them."

The spirit of the Anxi army brought tears to my eyes.

The city is filled with white-haired people; they will never return to their hometown until death.

I look up and see the sun, but I cannot see Chang'an.

……

"Does anyone have a question now?"

"Why is there another boss spawning on our Chinese border?"

Moreover, each one was stronger than the last. Before the An Lushan Rebellion, they were able to fight the Tang Dynasty on equal terms, and after the rebellion, they became even more formidable, directly attacking Chang'an and capturing Chengdu.

A map appeared in the sky, showing the rise of the three regimes—Tibet, Nanzhao, and Uyghur—almost perfectly coinciding with the decline of the Tang Dynasty.

"The answer is actually quite simple: the border troubles of the Tang Dynasty were self-inflicted."

It wasn't that the foreign races suddenly became stronger; it was the Tang Dynasty that made them stronger.

She opened the timeline of Tibet.

The rise of Tibet was directly related to the technological output of the Tang Dynasty.

When Princess Wencheng entered Tibet, she brought not only Buddhist statues and scriptures, but also agricultural techniques, textile techniques, medicine, and calendar systems.

Songtsen Gampo used these technologies to complete the internal integration of Tibet, transforming a group of scattered tribes into a unified empire.

Moreover, the Tang Dynasty made extensive use of non-Han soldiers and generals, spreading the most advanced iron smelting, city building, and siege technologies.

By the time of Emperor Gaozong of Tang, Tibet had developed a complete administrative system and a powerful cavalry army.

In the Battle of Dafeichuan, Xue Rengui's 100,000-strong army was completely wiped out, and from then on, the Tang Dynasty and Tibet engaged in a protracted war in Hexi and Longyou for two hundred years.

They're no longer the savages roaming the grasslands; while you're developing, they're developing too.

The Tubo, Nanzhao, and Uyghur regimes were no longer the loosely organized nomadic tribes of the early Han and Tang dynasties. They had their own administrative systems, military organizations, and economic foundations.

The Tang Dynasty spent over a century exporting its technology, systems, and culture to its neighbors, only to be devoured by them in return.

[Technology export has fostered a formidable enemy]

Why give them the technology?

Longyou was the largest military horse breeding ground in the Tang Dynasty. The fall of the horse breeding ground was tantamount to the complete isolation of the cavalry.

……

Li Shimin looked at the lost dynamic map of the Western Regions, at the Anxi Protectorate which had been isolated in a remote region for more than forty years, and at the white-haired veterans who had never been able to return to the Central Plains until their deaths. His hands clenched into fists in his sleeves, his knuckles turning white.

He knew that it was now his era's turn to be put on the hot seat.

Technology export... has created a formidable enemy.

Those who come after him discuss a historical event that has already occurred: his reign of Zhenguan, and how he sent Princess Wencheng to Tibet.

"Your Majesty." Fang Xuanling's voice broke the silence. He stepped forward and bowed. "What Tianmu said is not Your Majesty's responsibility alone. Princess Wencheng's journey to Tibet was a strategy devised by me. If we discuss the success or failure of the strategy, I should share the responsibility."

Li Shimin did not turn around. "Minister Fang, I am not here to assign blame. I am reflecting on whether my decision to send Princess Wencheng to Tibet was right or wrong."

Wei Zheng stepped forward, his voice neither humble nor arrogant, "Your Majesty, I believe that sending Princess Wencheng to Tibet was a wise move given the circumstances at the time. Tibet had already moved from a loose tribal alliance to unification, and this was something the Tang Dynasty could not control."

"But it was also the Tang Dynasty that gave it a push from behind." Li Shimin continued, his tone devoid of anger, only displaying a calm, almost cold, self-examination.

"I know that I did consider this consequence back then, but given the circumstances at the time, I had no better choice. I had just ascended the throne, the country was newly settled, and the Turks were still eyeing us covetously from the north."

If I had not sent Princess Wencheng to Tibet and had not supported Songtsen Gampo, Tibet might have sided with the Turks.

At that time, the Tang Dynasty faced a two-front war, north and south, a gamble I could not afford.

Li Jing stepped forward and said, “Your Majesty, I have led troops in the Northwest for many years and know well the treacherous terrain of Tibet. Tibet occupies the Qinghai-Tibet Plateau, a high-altitude and cold region that is easy to defend and difficult to attack. If a large army goes deep into the region, altitude sickness alone can cause more than half of the soldiers to be lost. With the strength of the Tang Dynasty at that time, it was impossible to destroy Tibet. Even if I personally led the troops there, I would not be confident of victory.”

"Therefore, I chose appeasement," Li Shimin said.

"It's not appeasement, it's control," Fang Xuanling corrected.

"Control," Li Shimin repeated the word.

The policy of "tributary relations" was a fundamental national policy of the Tang Dynasty towards neighboring ethnic groups. Through marriage alliances, investiture, trade, and technology transfer, the Tang Dynasty incorporated these groups into its tributary system, making them vassals rather than enemies.

Tibet, Uyghur, Nanzhao, Turks, and Khitan were all once included in this system.

"The strategy of appeasement is essentially about exchanging technology for peace and cultural export for military security. I give them technology, culture, and institutional models, allowing them to transform from tribes into empires. Then, through marriage alliances, investiture, and trade, I bind them to the Tang Dynasty's system."

He paused suddenly, his voice lowering, "But Tianmu is right. If you give them the technology, they will eventually use it to turn against you. That's the price of control. But back then, we couldn't have imagined that the Tang Dynasty would encounter the An Lushan Rebellion."

Silence fell over the hall. The Zhenguan era was not achieved solely through warfare, but also through effective governance.

Turn potential enemies into vassals and maintain maximum peace at minimal cost.

However, this also sowed the seeds of future problems for the empire; if it weakened, it would be vulnerable to attack.

How did the Tang Dynasty collapse?

Li Shimin turned around and looked at the assembled officials in the hall.

His gaze swept across the faces of Fang Xuanling, Wei Zheng, and Li Jing.

"Minister Fang, draft an edict: from this day forward, the Tang Dynasty's technology exports to its vassal states must have boundaries."

Agriculture and textiles can be given, and medicine and calendars can be taught, but core military technologies, iron smelting formulas, bow-making techniques, and blueprints for siege weapons are all prohibited and must not be circulated.

Furthermore, border checkpoints bordering India and Tibet strengthened the inspection of military equipment leaving the country.

Fang Xuanling bowed deeply: "Your subject obeys the decree."