Since no one's interested in taking this, I decided to give it a try. I haven't done any proper writing after highschool and English isn't my native language, so don't give too much expectation:
January, 200 BC
The Emperor has been pacing restlessly for hours now. His patience is now like the tent around him: too small for a man of his status, and seems to be shrinking every moment. 7, 6, 5, it takes less and less steps to circle the tent, as he paces even faster. The cold has froze off the fingers of many soldiers, but even that isn't enough to cool his head now. He had ordered the guards out of his tent at noon, and that no one is to disturb him without a better way to break through the Xiongnu horde surrounding this mountain.
In another tent, the Emperor's chief adviser, marquess Chen Ping is struggling to sent plan C into motion.
Plan A was to tell the Emperor to give up chasing the Xiongnu army two weeks back, but victory disease had caught up with the Man and the unfortunate Liu Jing, who said it before he did, took the flak head on and is now in a cell block in Guangwu — where he has food other than grass, water other than melted snow, thick walls that protect him from the cold and is not on the Xiongnu chopping board right now — oh the irony.
Plan B was conceived to get themselves out of this mess in one piece. The Emperor only made it to what he is now by being open to suggestions in the face of adversities, and the lethal tactical mistake of pursuing full speed without the infantry cured his victory disease before he committed any irreversible mistakes. The summary of this plan is simple: bribe one of Modu's wives and had her tell Modu to let them go. The execution is far more complex, involving infiltrating the Xiongnu army to the Chanyu's complex at night and snuck back before dawn. It took several skirmishes to complete an unbloodied set of Xiongnu attire, and good luck to have some bribable allied tribesmen instead of Modu's personal guard stand on watch. The message is to state that Chanyu is the lord of the steppe grazing land, while the Emperor only keeps his farmlands that are of little use to nomadic people like the Xiongnu, and woven with Xiongnu pride that they should always be the masters of the steppes on horseback, never sedentary peasants bound to a puny piece of land for life.*
It went smoother than expected, the report from the agent is that the pillow talk did move Modu, who said he will make up his judgement today. As dusk approaches, however, both the Emperor and Chen started worrying for they both knew that they are completely at the Chanyu's mercy. While the soldiers may be willing to fight to the death to have one less barbarian raiding their hometown, they won't last more than a few hours if faced with an all-out assault. Plan C is a crude one: charge down the mountain after dark to link up with the infantry on the other side, anvilling any Xiongnu who stand between them. Though costly, it's the only way to get out alive if Modu is determined to eliminate them. It's not possible to signal the infantry after sunset, so to coordinate an attack at night, a courier must sneak through the enemy line shortly after night falls. But once the order is sent, there's no turning back…
"Marquess! Urgency! You won't believe this even if I said so! Please come out and see it with your own eyes!" The shout of a guardsman outside disrupted his thought, but could it be…
The clamor outside is becoming unbearable for the Emperor. He didn't pay any attention at first, believing that it isn't anything important in this situation, as the guards will pass anything newsworthy to him. As the noise became louder and louder, it soon became unnerving. "I said don't disturb me without a way to get out of here" he speaks to himself, "are they talking about how we are not going out of this place? Else they would've told me!" his mind is strained like the sinew of a cranked crossbow, about to go at anymore pressure. Suddenly, he hears Chen Ping's voice coming from outside the tent. He tries to act calm when Chen entered, and says: "I believe you have a good reason for disturbing the Emperor?" Chen, doing a kowtow, replied: "Your Majesty, reinforcements have arrived from the south, but…" "Go on." Gaozu commands, to which Chen asks the Emperor to see it for himself, as mere words aren't convincing.
Upon seeing what Chen wants him to see, the Emperor collapses like an unstringed marionette, sitting on the dirt without any dignity. Further south of the Han infantry behind the Xiongnu lines, banners of Han Xin, the renegade King of Hán, fly high. Now that the Han infantry is sandwiched too, the last hope of a sally is gone for good.*
Shortly after the sun completely set, Xiongnu couriers delivered the message calling for negotiation, to which Gaozu almost stared them to death, but had no option but accept. The final treaty, sealed the next day, is the biggest humiliation Xiongnu ever did to a Chinese ruler to this point. Leaving out the minor details, the Peace of Baideng consists of these three main articles:
1. Xiongnu and Han, from now on, respects each other's living space. Any Han city occupied by Xiongnu must be returned to Han at once. Similarly, the traditional Xiongnu pasture by the Yellow River, taken by Qin, must be returned to the Xiongnu people, along with all fortifications therewith at once.
2. The Kingdom of Hán is, from now on, no longer a vassal of the Emperor of Han, but a vassal of the Chanyu. Land of the Kingdom of Hán, including thosd ceded to the Chanyu before this treaty, is not to be considered a part of the Empire Han, and any Hán cities occupied by Han must be returned at once.
3. The army of Xiongnu and Hán is responsible of the safety of every man of the Han army until it enters Han territory safely.
Because Modu didn't take any land that wasn't part of Hán before the war, 1&2 basically entitle him to all his conquests, and 3 is essentially parading the Emperor through the cities along the way.
Red is territory firmly Xiongnu before the war, red stripes are the gains in this war. The murky "traditional Xiongnu pasture" is not shown.
