"If the enemy does not come, we must make them come. Their defeat of Silla's raiding fleet means their navy has grown stronger. While the border is sealed by Goryeo, the navy can still operate freely. If the main forces of Gaegyeong are absent, wouldn't Baekje try to take advantage? Even if they come and kill both me and the queen, the Baekje army will be annihilated, and the benefits will be ours."
Da In-seon had already prepared the stage for Baekje to act exactly as he wanted.
In reality, the border region between Baekje and Goryeo was tense, with both armies facing off, while Silla was preparing troops to launch a counterattack. In this situation, the only truly free force was Baekje's navy, recently reinforced to overcome the raiding fleet.
The commanders present could hardly breathe at Da In-seon's audacious plan. It seemed absurd at first glance, but in truth, it was a strategy that could decisively seize control of the Three Hans for Baekje.
Da In-seon had always toyed with his opponents in war. Surely, he had some hidden reason for guiding the Baekje army into this position.
Complacency was dangerous, but Da In-seon's strategies were consistently perfect, leaving his commanders both wary and intrigued about what extraordinary plan he would unveil next.
"If they come, where will they arrive?"
"The Yesong River, most likely. They'll land there, strike Songak quickly, and retreat. Even if they do not bring tens of thousands, they'll bring enough to seize Songak and threaten our necks."
Da In-seon estimated that Baekje could muster around five to ten thousand troops for a landing at the Yesong River. That number was enough to take the relatively unguarded Gaegyeong, carry out plundering, arson, and attempt to assassinate both Da In-seon and Queen Jinseong before retreating safely.
"I see… then Your Majesty intends to be the bait yourself?"
"I will ambush them at the predicted landing point along the Yesong River. If we deploy even the Cheonja Cannons, all the better."
Thanks to Choi Dong-sun's efforts, Goryeo had completed the development of the Cheonja Cannons. While their immediate performance was limited, they were enough to startle and repel the enemy. With continued efforts and sufficient sulfur, the Goryeo army would soon be fully armed with gunpowder weapons.
The commanders of the Eight Banner Army, however, still lacked detailed knowledge of the cannons. Though gun platforms were established, the soldiers assigned to operate them had little practical experience. Thus, Da In-seon planned to personally demonstrate their operation to ensure future coordination between the cannons and the Eight Banner forces.
Of course, the Eight Banner commanders also harbored a private desire to stop Baekje's landing themselves. Many had fought in the Uyghur region and clashed repeatedly with Liaodong forces over the years—they were seasoned veterans.
"What shall we do, then?"
"The designated commanders will move south and confront the Baekje forces. As for the others, I will personally demonstrate the operation of the cannons."
Though unable to participate directly in battle was frustrating, the Eight Banner commanders were eager to witness the might of the cannon corps firsthand. They had seen training in the capital and Gaegyeong, but observing their power on a real battlefield was a rare opportunity.
'Continuously purchasing sulfur is a burden. Luckily, we know that sulfur can be sourced from Gyeongju, Chungcheong, and Gyeonggi provinces. We can supply it ourselves. Baekje remains a troublesome curiosity.'
Thanks to Yi Jae-chun's continued procurement of sulfur, Choi Dong-sun confidently combined saltpeter and charcoal to churn out gunpowder. The financial burden was minor, and producing locally avoided unnecessary expense.
For Da In-seon's audacious strategy, all main forces except the cannon corps and a portion of the Eight Banner Army were stationed along the Baekje border.
The commanders assigned to this border duty, including Park Sul-hee, were secretly displeased. Yet Da In-seon's granting of "discretion" drew smiles to their lips.
He had commanded them: "Harass the Baekje border freely, but avoid full-scale battle."
As soon as the order was given, the Eight Banner forces struck like fish in water, engaging Baekje along the border.
"What army is that?"
"The mighty soldiers of Goryeo! Strike the Baekje scum!"
"G-Goryeo forces! General…!"
The Eight Banner Army launched relentless attacks, capturing Yeonsanjin and fighting in Yesan, Cheongju, and Jomulsung, cutting down thousands of Baekje soldiers before retreating.
Caught off guard, Baekje's forces scrambled, needing to pull their main troops north from the Silla border. But the Eight Banner Army only hit and ran. Their rapid maneuvers left the Baekje forces disoriented.
The Goryeo army provoked Baekje just enough without pursuing, minimizing losses while instilling the impression in Gyeon Hwon that "your army is my toy." The Baekje court seethed with anger at Da In-seon.
"What? That Da In-seon dares provoke me! Taking land from weak Silla while inflating his own power!"
"Indeed, Your Majesty! They must be punished!"
"Indeed, Your Majesty! They claim to be Goryeo, but they are a nation of Malgal! In the past, Silla sold Goguryeo lands, and now they sell their own to pursue peace! Da In-seon must be defeated!"
Baekje's court erupted in fury. Their national system was in place, and they were ready to challenge Silla. Yet they never anticipated Goryeo's forces would strike so quickly. Furthermore, Gyeon Hwon did not even know the full strength of Goryeo's army.
"Still, they are avoiding full-scale engagement, correct?"
"Yes, Your Majesty. Perhaps they lack sufficient forces."
Indeed, Baekje interpreted Goryeo's hit-and-run tactics as the actions of a smaller force. Their assumption was correct: the only elite troops Goryeo had on site were the cannon corps and a portion of the Eight Banner Army.
"Will the Tang crown me as King of Baekje?"
"No answer yet, but likely so."
Upon hearing that Da In-seon had been recognized by Tang as King of Goryeo, Gyeon Hwon hastily sent an envoy to Tang. The result, however, was unfavorable.
Tang needed Goryeo's cooperation to keep regional powers in check. Crowning Gyeon Hwon as king of a Goryeo enemy might offend Goryeo. Ignoring a vassal's request, however, would undermine the emperor's authority. Thus, Tang procrastinated.
If Tang recognized Baekje, it could assert itself as a dominant force in the Three Hans. With recognition delayed, Gyeon Hwon lamented.
"What if we involve Japan?"
"You mean request reinforcements?"
By the time Goryeo moved, Later Baekje was isolated. Even if Silla did not act, the dual pressure from both sides created strain.
"Silla drew Goryeo in; why shouldn't we? Japan's royal family is related to old Baekje, and the name 'Japan' itself comes from Baekje. Our nation inherits Baekje, so seeking help is reasonable."
In 660, Ye Sik-jin and Ye-gun took the Baekje king to Tang, erasing Baekje from history. The tomb inscription of Ye-gun referred to Baekje as Japan and Wa as Fusang, indicating deep historical ties.
Gyeon Hwon decided that Japan could provide support due to these old connections.
"Should we not present reasonable conditions as well?"
"What if we cede Silla?"
"You mean… give the lands of the Three Hans to Japan?"
Neunghwan, unsure of Gyeon Hwon's intention, asked, while Gyeon Hwon tapped the armrest of his throne thoughtfully.
"After pushing Goryeo back to the Yalu River, we can expel the Japanese from Silla's lands once the war ends."
"And if Goryeo and Japan form an alliance?"
Neunghwan recalled that in the past, Japan allied with Balhae to conquer Silla. Though it failed, if Goryeo and Japan both opposed Baekje, it would not be favorable. Yet Gyeon Hwon focused only on the immediate situation.
"Japan can guard the seas, and we can check Goryeo along the Yalu River. If we control Gaegyeong, they cannot act freely. Even if Tang is weak, would they allow Goryeo to expand unchecked? They might mediate or strike Liaodong—have we not fought Tang there before?"
"Indeed, Your Majesty."
Most officials supported this plan.
However, some were concerned about involving Japan. Neunghwan frowned slightly, though the decision was final.
"Of course, this is for extreme situations. We are not yet pressed that far."
"Yes, Your Majesty. First, we will send all troops along Silla's border to Goryeo's frontier."
Later Baekje, pressured by Goryeo, moved its troops from Silla's border to confront Goryeo. Especially at Jomulsung and Imjon, where Goryeo provocation was intense, Baekje stationed its main forces.
The Baekje military kept vigilant, conducting reconnaissance, and discovered that Gaegyeong was nearly undefended. They also learned that Da In-seon and Queen Jinseong were present.
An emergency alert shook Baekje.
"Your Majesty! Urgent news!"
"What is it?"
"The main forces have left Gaegyeong, and the Silla queen and Goryeo king are there!"
Gyeon Hwon had already heard that the Goryeo king was in Gaegyeong, but learning that the Silla queen was also there and the city was nearly empty stunned the Baekje court.
The Silla queen represented a thousand-year kingdom. Even though she was incompetent, her presence with Da In-seon was unfavorable for Gyeon Hwon.
With Gaegyeong nearly undefended and only a few thousand troops present, it was a tempting opportunity.
If Gaegyeong fell, Later Baekje could reverse its fortunes and seize dominance over the Three Kingdoms.
Upon hearing of Gaegyeong's vulnerability, Gyeon Hwon resolved decisively.
"If their forces are truly small, we can gamble. Using our navy, we can land downstream at the Yesong River and strike Gaegyeong easily."
"An excellent strategy, Your Majesty."
Before Goryeo reinforcements arrived, Gyeon Hwon moved swiftly.
"Very well. Shall General Sang-gwi lead this operation?"
"If Your Majesty grants me the chance, I will cut down Da In-seon and the Silla queen immediately! Just give the command!"
"Good. You must be itching for action. Go ahead."
"I will prepare at once."
Without hesitation, Later Baekje assigned General Sang-gwi to lead the navy to strike Songak under royal command.