Li Shimin had no interest in playing the long game with the Tibetan Empire.
Slow and steady was for turtles, not for a man like him. He had conquered half the known world before the age of thirty, as history would remember him: fast and unstoppable.
He had no intention of sitting idle while the mountain dwellers overreached and choked on their own ambition.
In the Tang Dynasty's original history, the court had paid little heed to the rising power on the plateau. They simply lacked knowledge of the threat festering beyond the peaks.
Ignorance bred complacency, and complacency allowed fangs to sink in at the throat.
But now the danger stood revealed, all thanks to the Light Screen. Every part of the threat was laid out plain. Every detail understood. And once you knew exactly what you faced, a threat became nothing more than a problem with a deadline.
As for the actual battle plan, Duke of Wei, Li Jing, already had everything mapped out behind that characteristically unreadable expression of his. Li Shimin trusted him the way you trust gravity. No need to double-check. You never question it. It just works.
So the Emperor of Great Tang turned his attention to other matters.
The imperial examinations had just concluded, and this year everything was bigger, with more candidates and more subjects than ever before. The MVP of the whole affair, the blind grading system, was finally up and running, with all names sealed so that no one knew who wrote which exam until the final scores were carved in stone.
It was Wen Mang's idea, pulled straight from the Lightscreen and followed down to the last detail.
The results spoke for themselves.
Every scholar who had walked all the way to Chang'an on worn-out sandals and borrowed coins sang the system's praises. The great aristocratic families put up about as much resistance as a soaked napkin.
The aristocratic families had not resisted as fiercely as Li Shimin had expected, although the reasons were hardly mysterious.
Illig Qaghan was right inside the imperial palace, dancing for the Emperor whenever called upon. The man who once commanded a hundred thousand fierce riders now spun around on command like a court entertainer, and any noble foolish enough to speak out against Li Shimin had to wonder if they wanted to end up looking worse than a defeated khagan.
The powerful clans were all gathered far away in the Qilu region, hundreds of miles to the east, and sending angry letters to Chang'an took serious effort. Getting Li Shimin to actually read them was nothing short of a miracle. More importantly, Li Shimin had not yet touched the Menyin system, that old "legacy admission" deal where sons got jobs just because their fathers held rank.
As long as he left that privilege untouched, most of them saw little reason to risk open resistance.
But Li Shimin knew he had only won one battle. The real war was far from over.
Think of it like a blacksmith working steel.
These scholars from humble backgrounds, picked purely on skill, were the finest raw iron around. Shape them with care, and they would become blades sharp enough to carry his will across the world. If the scholars were raw iron, then Fang Xuanling and Du Ruhui were Longquan and Tai'e, legendary blades that needed no reforging, only a worthy target.
Lately though, those two seemed unusually busy.
Just then a eunuch appeared at the door. "Your Majesty, the Duke of Liang and the Duke of Cai request a joint audience."
The fact that they had come together, and without prior notice, immediately caught Li Shimin's attention. Fang Xuanling and Du Ruhui never dropped by without good reason.
As Chancellors and Dukes, they did not need to jump through hoops to see the Emperor. A word to the eunuch, a nod from the throne, and the doors opened straight away.
They were ushered into the Ganlu Hall.
Taiji Palace had been renovated long ago, but the court still found it odd that the Emperor spent most days here instead of the main hall unless there was a formal gathering.
Fang Xuanling and Du Ruhui knew exactly why.
The moment you walked in, your eyes went straight to the scroll hanging dead center. Written in Li Shimin's own hand was the Song of the Lady of Qin, and it faced every visitor like a challenge.
Both men could recite the verses backward, but that did not make them any easier to read.
Every line felt like a thumb pressing into a bruise. Hanging it right where no one could miss it was the Emperor's way of keeping himself sharp, never letting himself grow complacent.
Around it hung the Map of Terrestrial Borders, charts of the Far Eastern Islands, a globe of the world, detailed schematics of crossbows and siege engines, a painting of Sleepless Chang'an, and an image of the Pagoda Bearing Heavenly King with unblinking eyes.
No wonder he practically lived here.
All this could spark a hundred ideas before breakfast, and half of these would give your average court official a heart attack if displayed in the main Taiji Hall.
Fang Xuanling's mind drifted for a moment. The future still haunted his dreams, and waking up was the hard part, but once he was on his feet, he tackled paperwork with a fierce intensity that startled even his own aides. Du Ruhui's take was much simpler. Without the Light Screen, he would be what the young people from the future called completely toast. No do-overs, no second chances. Just drop dead.
They did not waste time on pleasantries. They simply bowed and presented a thick report bound in fine silk.
"Ruhui and I spent over a month compiling the ledgers for Hu County. We humbly ask Your Majesty to go through it."
Fang Xuanling's face looked heavy. This was not the put-on seriousness you faked for court meetings. This was the real weight of someone who had stared at rows of numbers that ruined his sleep for a week straight.
With both hands, Li Shimin took the scroll and opened it. A wall of figures hit him, so dense that his vision blurred for a second.
What in the world...
After steadying himself, he forced his attention back onto the report.
Hu County sat about forty miles southwest of Chang'an, close enough that all its census records had been kept in the capital ever since the chaotic split of the Northern and Southern Dynasties. Even Sui dynasty era data had survived untouched. A complete fossil record of the region's history on paper.
The report opened with the fifth year of Kaihuang, the early Sui Dynasty's founding years, and it laid everything out plain. Total farmland under cultivation. Total registered households. Then came the part that made Li Shimin's breath catch: simple division. Average fertile land per household. The same calculation was repeated for the third year of Daye, the first year of Wude, and the second year of Zhenguan. Four points in time, four averages, lined up in a single column.
Li Shimin stared at the four figures for a long moment, but the conclusion required no interpretation because the numbers spoke for themselves. The third year of Daye marked the Sui Dynasty at its height, glorious and powerful, with the empire standing at its absolute peak, yet the average land each family held was lower than the baseline set back in Kaihuang's early years. These were just clean records on paper that did not even account for the way wealthy families quietly swallowed up small plots until ordinary farmers had nothing left to call their own, and even without factoring that in, the result screamed loud and clear.
The Sui had looked so glorious and powerful at its height, but the numbers told the ugly truth. The average farmer's plot had actually grown smaller. All the wealth flowed upward and never trickled down. Empty bellies never stayed that way forever. Sooner or later, hungry men grabbed torches and sharpened pitchforks, and that was always how the chaos started. Li Shimin had lived through it himself. He had ridden across the ruined countryside and seen the full wreckage with his own eyes.
His fingers tightened around the scroll, and a cold shiver ran down his spine that had nothing to do with the evening air.
Other ministers had laid out figures for him before, but never like this. One simple average, repeated across four different time periods, had torn away every comforting excuse. There was no room left for fancy words or hollow claims.
Now Li Shimin finally understood why the Light Screen had called mathematics the King of Sciences.
One bright spot: the numbers from Wude Year One to Zhenguan Year Two were not a disaster. Farmland was growing again, the population was recovering, and the chart pointed in the right direction. But a problem was hiding underneath. The gap between Kaihuang (the 580s and 590s) and Daye (the 600s and early 610s) was twenty years, while Wude (the late 610s to 620s) to Zhenguan (the 620s to 640s) was only eleven, so the comparison was not exactly fair. And then there was Hu County. The soil along the Lao River was rich, no doubt, but the land itself could not grow. That valley had a hard limit on how much it could produce. The land stopped expanding, but people did not, and Li Shimin could now see the danger in that simple equation.
The contradiction hit him like a punch to the gut. The land could only produce so much, but people kept having more children. He had heard about this on the Light Screen. The Malthusian Trap, they called it. Back then, it felt like some distant academic problem, just theory, nothing to lose sleep over. But now the numbers were right in front of him. They did not guarantee the Tang would collapse in a century. They just showed him the path the empire was walking, and it was not a good one.
"Xuanling. Ruhui." His voice came out softer than he intended. "What you have done for this dynasty is beyond measure."
Fang Xuanling waved his hands quickly. "Your Majesty is too kind. We only organized what was already there."
Du Ruhui added, "The real work was done by the clerks who kept the records for decades."
Li Shimin fixed them with a look. "And yet no one before you thought to actually read them." He paused. "So stop deflecting. You earned this."
Then Li Shimin turned the page, and the next part was even worse. The numbers grew denser, the tables multiplied, and some were even tucked inside other tables. He recognized every single character and understood every word written there, yet the meaning continued to slip through his fingers like fish darting under dark water.
For heaven's sake, he thought, is this a report or a punishment?
He slowed right down and chewed every sentence like it was tough jerky, working through it word by word, line by line. By the time he reached the final table, Li Shimin had been through a baptism by mathematics, the kind that teaches you one thing above all else: if there is an easy way, take it. This was definitely not it.
A eunuch slipped in, lit the evening lamps, then slipped out again.
Voices drifted in from outside. Chengqian and Li Tai chatting, then little Li Zhi whining about something. Probably dinner. Probably a toy. Probably just the fundamental unfairness of being the youngest.
They reached the Ganlu Hall doors, exchanged a few quiet words with the guards, then their footsteps faded into the distance.
Fang and Du stood like carved statues. Posture straight. Not a single fidget. Every now and then they glanced up at the Song of the Lady of Qin hanging on the wall. In the flickering light the characters looked almost like they were weeping ink.
Dinner was brought in, taken away, reheated, set down again, carried off once more, and heated all over a second time.
The eunuch was just about to bring it back for the third round when Li Shimin finally let out a long heavy breath, the kind that rises all the way from deep in your chest.
"So that is how things really stand."
He set the scroll down and looked straight at his two ministers. "The richer the state grows, the poorer the people become."
Fang Xuanling and Du Ruhui bowed low, ignoring the ache rising in their knees from standing so long.
This was exactly why they served this man.
When he first took the throne, no one dared say it aloud, but half the court had secretly hoped that the Tiance General would trip over his own feet as Emperor.
Everyone knew the old saying: you could conquer the world from horseback, but you could not rule it from there.
Yet this former general had climbed down from his saddle. Calmly and deliberately, he had taken up the tools of governance with the same steady grip he once used to hold a spear, and he balanced military strength and civil order like he had been born to do both.
He did not know everything, but he never stopped pushing and never stopped learning. He never begrudged sitting three hours straight staring at rows of numbers until his eyes burned, because he understood that the truth lived in those figures.
Li Shimin solemnly bowed back to his two pillars of the empire. Then he tucked the heavy memorial securely into his robes. Only then did he finally realize his stomach was loudly protesting in hunger.
"Stay and eat with me," he said.
The two ministers exchanged a glance. Fang Xuanling smiled faintly. "Your Majesty is too kind."
---
After the meal, a wildly excited Li Shimin rushed straight into the inner palace, heading directly to Empress Zhangsun's quarters.
He could not wait to share these explosive new thoughts with his beloved Guanyinbi.
"The richer the state, the poorer the people? What kind of twisted logic is that?" Empress Zhangsun asked, baffled.
"If there are no wars or chaos, how many children can one common household give birth to?" Li Shimin asked in return.
Empress Zhangsun was actually quite knowledgeable about this.
"When encountering war and chaos, families are destitute. They will often choose to have more sons to increase their manual labor force. However, infant girls are hard to keep alive, and the drowning of female infants is common. In the end, a household might perhaps raise three sons."
"But if it is a prosperous, peaceful era, an ordinary common household will likely raise three to five sons and two to three daughters."
Li Shimin nodded slowly. He continued his questioning.
"Then... what happens a hundred years into a prosperous, peaceful era?"
Author Note: The "Malthusian Trap" is real and it's terrifying. Every agrarian empire in human history hit the same wall: population outgrows arable land, and the correction is always famine, plague, or war. The Tang Dynasty's actual solution was... well, they didn't have one. They just rode the wave until it broke. In this timeline, Li Shimin has the math. Whether that's enough? We'll find out.)