However, Sejo strengthened the centralized system and reduced northern officials, which made Yi feel uneasy about his position.

[2] He stirred public sentiment by spreading rumors that soldiers from Pyeongan and Hwanghae would also cross Seolhanryeong Pass and enter Hamgil.

[4][1][2] Yi Si-ae established his base in his home, Kilju County, and then led his rebel army with the Iksok Force (Iksokgun, Korean: 익속군; Hanja: 守城軍) as the vanguard to attack Bukcheong, and Hongwon counties, and Dancheon, Hamhung cities and murdered all the local officials dispatched from the central government, such as provincial governor Shin Myeon, and captured Yoon Ja-un claiming he received the King's command to execute them for treason.

On the other hand, Yi Si-ae gathered power by propagating to the people of Hamgil that his rebellion was the cause of the execution of Kang Hyo-moon and others according to the will of King Sejo.

In the early days of the rebellion, the people believed Yi's rumors and persuasion that Kang was a loyalist and that the army that came to subdue him was rather a traitor.

Still, he barely moved to Hoeyang County because the rebels were too strong, especially the Iksok Force, which numbered 4,500, with 900 of them armed with chongtong as they had years of experience fending off Jurchen raids.

King Sejo, in response, dispatched more reinforcements to the Subjugation Army and made the provincial governor Kang Soon as general-in-chief of the Northwestern Frontier District and gave him command of 3,000 troops from Pyeongan to Yeongheung County and Muncheon City.

"I hereby send you three mortars (碗口), 250 chongtong, five hwachas, 400 hwa-jeon (火箭, gunpowder launched arrows), 27 geun (斤) of gunpowder (16 kg), 1,000 gakgung (角弓, a type of bow), and 5,000 bowstrings ..."The troops of Prince Gwiseong repulsed Yi Si-ae's forces in Anbyeon and advanced to Hoeyang through the Cheollyeong Pass.

Meanwhile, King Sejo sent down various filial piety statements (Hyoyumun, Korean: 효유문; Hanja: 曉諭文), setting the condition that would pardon the rebels if they surrendered even now.

King Sejo ended the filial piety policy, freeing high-ranking officials such as Shin Suk-Ju, and at the same time devised hard-line measures against the rebels.

Bewildered by King Sejo's strict standards, Yi Si-ae retreated from Hamheung and moved its headquarters to Dabo Village in Bukcheong to use it as a base.

Kang Soon made Guseong County the spearhead of the attack on Bukcheong and had him build a camp at Yangryeong, Sangaeryeong, and Jonggaeryeong Passes.

Accordingly, Kang Soon-Eun, along with Park Jung-seon, Heo Jong, and Eo Yu-so, crossed Jonggaeryeong Pass and encamped in front of Bukcheong.

He dispatched a group of 500 female rebels to attack the government forces from Gosaripo Village in Iseong County to Bukcheong Fortress.

Buksan and surrounded and advanced from four sides toward Manryeong to attack Yi Si-ae simultaneously, exchanging fire with their gunpowder weapons and arrows.

At the same time, around 5-7 pm, Eo Yu-so ordered the bombardment of the middle peak using hwachas penetrating the left flank of Yi Si-ae's army.

[2][4][1][3] The next day, August 1, the government forces pursued the Yi Si-ae troops fleeing north to Iseong County, burning guesthouses and warehouses along the way.

On August 8, Prince Gwiseong and the government forces crossed Maunryeong and advanced to Yeongjewon, while Yi Si-ae encamped in Dancheon and attempted resistance across Namdaecheon but retreated to Kilju.

Yi Si-ae was executed by a thousand cuts which ended the four-month rebellion, and the military carried his head to Hanseong.

[2] The Battle of Manryeong was the turning point in the rebellion where both sides engaged in the first massive fire combat in the Joseon Dynasty.