The Dongjin Expedition
Of course, there were those who didn't surrender, but most just wanted to stay neutral, and the number of Jurchens who actually raised arms against us was negligible. We simply left the northern territories of Dongjin alone since it was hard to send forces there.
In any case, with the surrendered Jurchen generals reorganized as Goryeo commanders and given troops, we assembled an army of 100,000.
"Is Yodong really such an easy region to conquer?"
"It's all about the era you're born into, isn't it, my lord? Dongjin is just a big eggshell, and Yodong has been in constant chaos due to its bat-like diplomacy toward the P'o Sŏn-mann'o and the Mongols. Now that Goryeo has crushed the Mongols amid all this, they have no choice but to surrender."
In original history, the Jurchen conquests were against a powerful Jurchen federation, and the Yodong campaigns were tough because the Ming were strong. But during King Gongmin's time, Goryeo had briefly held Yodong, and that precedent made the current tangle of Khitans, Jurchens, and Mongols ripe for Goryeo to seize Yodong.
Of course, this conquest wasn't a full takeover of Yodong, but destroying Dongjin would at least let us claim, "Ah, we've achieved our national policy of northward expansion."
"Even the neutral regions are holding back from immediate surrender out of caution. We should strike straight for Yoyang."
Right now, there weren't many fortresses resisting to the death. Even if they sent reinforcements to aid P'o Sŏn-mann'o, we could just wrap things up before they arrived.
"Will that work?"
"They didn't send any army against us during our entire march here. That's as good as treason against P'o Sŏn-mann'o. If we smash Yoyang quickly, they'll surrender too."
Father and I saw eye to eye perfectly. He wanted to conquer Dongjin swiftly for the sake of the thousand-year Choe regime. Honestly, if we had more time, I'd have tried diplomacy with Dongjin. But with the Mongols' reaction unknown, we needed to eliminate this forward threat first. That's why I agreed with Father.
Our perfect alignment made this northward push smooth sailing. If Father had been overconfident in another way—thinking we could take the Mongols anytime and delaying the Yodong advance—we'd have been in big trouble.
"Even if it's possible now, what happens when the Mongols retaliate later?"
"Exactly. We've wiped out 30,000 of them, so they won't underestimate us, but won't they come back even stronger for revenge?"
The senior generals fretted over Mongol retaliation.
The Mongols will retaliate. But not yet—they lack the capacity. News will take time to spread, and once they learn we've annihilated 30,000 with a substantial force, they won't touch us until after they conquer Jin.
"To be safe, after taking Yoyang, we should plant minefields at key passes to harass them periodically. And for now, at least, the Mongols can't move."
A thorough massacre. We left no survivors on the level of the Gwiju Great Victory. Back then, barely a thousand out of 100,000 lived. Even if some hid and fled, reaching the steppes would be hell.
"First, we take the surrendered Jurchen reinforcements and attack Yoyang."
The subjugated ones knew we were coming for Yoyang and sent troops. Honestly, I saw this Dongjin campaign as a bit of a gamble. Not all Jurchens would surrender, and hitting Yoyang was a straight capital strike—like when the Khitans destroyed Balhae, or Sobaeap's third invasion of Goryeo, or the Qing's Bingziho Treaty era.
I wanted to show that such direct assaults weren't just for nomads. We had to do it before Dongjin could beg Mongol aid. That's why we'd brought every cannon and iron cannon unit, even if it strained us.
"Alright. Let's do it."
We first had the subjugated Dongjin generals merge with the Jurchen reinforcements. That alone gave us 20,000 Jurchens. Though mauled by the Mongols, they were nomads who'd troubled Goryeo plenty before. We rebuilt to 100,000 and marched on Yoyang.
Of course, P'o Sŏn-mann'o sent troops along the way. But they were routed, fled, or surrendered to our reinforced Jurchens and my Jurchen Byeolcho under Ugaha.
And so, we reached Yoyang.
Dongjin Yoyang
Yoyang, Dongjin's capital, was originally the Jin Eastern Capital. P'o Sŏn-mann'o, a Jin general, had founded Dongjin there after coming to crush rebels.
P'o Sŏn-mann'o had watched from afar during the Mongol invasion of Goryeo but often harassed us. He hadn't even heard of Goryeo's great victory over the Mongols before learning our northern army had seized several Dongjin fortresses—a sign we'd crushed the Mongols. It was agony for him.
"Damn it. How the hell did Goryeo beat the Mongols?"
Wasn't Goryeo the one cowering before Khitan remnants? He'd volunteered aid to the surprisingly successful Goryeo lately, and the Mongols had even granted him Yoyang. But now everything was going wrong.
No time to sit idle. While his guards held, requesting Mongol aid seemed best.
"Your Majesty! Goryeo forces are marching on Yoyang! At least 100,000 strong. Their vanguard cavalry, 10,000 horse, has begun the siege!"
But before he could beg the Mongols, Goryeo had advanced lightning-fast. With no time to flee, P'o Sŏn-mann'o's Dongjin flickered like a candle in the wind.
Jin Kaifeng
Around this time, word reached Jin's Kaifeng.
"Goryeo repelled the Mongols?"
"Yes, Your Majesty! 30,000 Mongols were annihilated at Gwiju, and their supreme commander Salitai fell to an arrow from Choi Yeon, daughter of the martial regent Choi U."
"What kind of fool dies by a woman's hand? Hah!"
We'd thought Goryeo a toothless tiger, but they'd achieved the impossible—slaughtering in open battle the Mongol army that had pushed even mighty Jin to this point. Not a huge force compared to our fronts, but besting 100,000 in the field meant Goryeo had reclaimed past glory.
This would burden the Mongols and split their eastern front.
"What is Goryeo doing now?"
"They're marching north to punish P'o Sŏn-mann'o, the Mongols' lackey."
In other words, Goryeo aimed to seize territory in this chance northward push. How to view this?
"Your Majesty, once they conquer P'o Sŏn-mann'o, send envoys to praise the Goryeo king and demand they withdraw."
"Goryeo served us as suzerain due to weakness, but they remember before we founded our state and resent us. Their eternal policy is reclaiming Goguryeo lands—they covet Dongjin. Chastise them sternly so they never eye Yodong again."
Was that realistic now? Sending envoys risked death at Mongol hands en route to Goryeo. Jin lacked strength even for that. We hadn't answered their aid pleas—how could we act?
"Realistically, if they covet Yodong, can we conquer Goryeo?"
The ministers fell silent at the emperor's words. Pushed by Mongols already, facing Goryeo's 100,000 expeditionary force—impossible. We'd have to break through Mongols first, then handle dual fronts with Goryeo, who'd beaten Mongols in the field. Jin couldn't. We were barely holding Mongols, gasping for breath. Antagonizing Goryeo too? Emperor Wan An Su-seo knew Mongol blades at his throat daily—he desperately needed allies.
Song stayed neutral, but they'd pinch us front and back if Mongols proposed alliance. Mongols weren't populous. If Goryeo just checked them from the east...
"Send envoys for now. We can decide later."
For now, Goryeo as ally. To preserve the state, no choice.
Before Yoyang, we held a war council.
"No time to offer surrender. We crush them with force so surrounding Jurchens submit too."
Scouts confirmed about 30,000 in Yoyang, per surrendered Dongjin generals—who also provided maps.
We bypassed east of the Taejah River plains, forded, and began the siege.
"As the artillery commander says, end it in days. Possible?"
"Once the assault starts, we'll infiltrate surrendered Jurchen generals to open from inside."
That would wrap it easily.
"Will P'o Sŏn-mann'o trust them?"
At a glance, it might seem like overconfident victory lap planning. But I saw high odds—he'd buy it. Our advance was unnaturally fast, like fleeing something, no looking back. Would he expect us prepping for next war?
"P'o Sŏn-mann'o has no choice. He'll crave reinforcements desperately. Plus, he won't suspect surrender to us."
No other path for him. He must hold somehow, so send the Jurchens. Open the gates inside, done.
"Why? Now's prime time to suspect—surrendering to open the way."
"P'o Sŏn-mann'o is a total bat. Came on court orders to crush rebels, founded Dongjin, fawns on Mongols while eyeing chances with Goryeo."
"What's that got to do with it?"
Desperation warps the mind. Psychologically, he'd cave. We're rushing before Mongols return to bulk up—same for him.
"Means he's that desperate. With us here so fast, he'll take reinforcements without question. Above all..."
Like Mongols underestimated us, so would Dongjin. When we crushed Khitan remnants, we left Kangdong Fortress garrisoned thin, looking pathetic to neighbors. That led here. Would he believe we toppled the world's Mongols?
Our fallen image—would bunker-bound P'o Sŏn-mann'o in Yoyang take it seriously? Frontier Dongjin generals might, but him?