Bruneian Civil War

The Bruneian Civil War (Perang Saudara Brunei and in Digmaang Sibil sa Brunay) was a civil war in the Bruneian Sultanate from 1660 to 1673. Between Abdul Hakkul Mubin and Muhyiddin. During Sultan Muhammad Ali's reign, a dispute led to the killing of Pengiran Muda Alam by Pengiran Muda Bongsu. In retaliation, Abdul Hakkul Mubin killed Muhammad Ali and declared himself the fourteenth sultan. A civil war ensued, with Abdul Hakkul Mubin fleeing to Kinarut. Sultan Muhyiddin sought help from the Sultan of Sulu, promising the area of Kimanis as a reward. As it turns out the Sulu Sultanate made a false claim over the entire Sabah. The dispute over eastern Sabah remains a legacy of this civil war.

Causes
During the reign of the thirteenth Sultan Muhammad Ali, there was a disagreement between the son of the Sultan, Pengiran Muda ("prince") Bongsu and Pengiran Muda Alam, the son of Pengiran Abdul Mubin over the results of a cockfight which Pengiran Muda Bungsu lost. His defeat was jeered by Pengiran Muda Alam. In his rage, Bongsu killed Pengiran Muda Alam and escaped from the scene.

In revenge, Abdul Hakkul Mubin and his followers garroted Sultan Muhammad Ali. Abdul Hakkul Mubin then made himself the fourteenth Sultan and took the title of "Sultan Abdul Hakkul Mubin". He tried to appease the previous Sultan's followers by appointing Muhammad Ali's grandson, Muhyiddin as the new Bendahara ("Chief Minister"). After a while, however, Muhammad Ali's supporters took revenge by convincing Bendahara Muhyiddin to stand up against Abdul Hakkul Mubin. Bendahara Muhyddin initially refused, but then later agreed to do so. His supporters started making disturbances in the form of poking spears into palaces and homes.

Sultan Abdul Hakkul Mubin then moved his palace to Cermin Island under the advice of Muhyiddin with the intent to wait the crisis out. After he left, however, Muhyiddin declared himself the fifteenth sultan. A battle between the two competing Sultans then ensued. Thus, the civil war of Brunei started.

War
During the civil war, Abdul Hakkul Mubin fled to Kinarut (in present-day Papar, Sabah, Malaysia) where, he stayed there for ten years, repelling repeated attacks by Sultan Muhyiddin. They returned to Brunei after a final attack by Muhyiddin's forces in which they failed to defeat Abdul Hakkul Mubin. It also noted that Muhyiddin finally defeated Abdul Hakkul Mubin in Cermin Island, using gunpowder they had purchased. This gunpowder originated from the Jambi Sultanate.

The Sulu army was supposed to help Muhyiddin forces in Cermin Island, but when they arrived the Sulu army in their ships arrived just to watch Muhyiddin forces fight Abdul Hakkul Mubin forces instead of helping the Muhyiddin forces, they landed after the battle to take war booty and to enslaved prisoners. This would infuriated Muhyiddin, who ordered the Sulu army to leave without giving eastern Sabah to them. Brunei denied giving eastern Sabah to the Sulu Sultanate. As there is no written evidence of the transfer.

Sulu claim narrative
Muhyiddin was concerned that the civil war was dragging on for too long and asked the help of the Sultan of Sulu to send for his forces. He reportedly promised the land of eastern Sabah as a reward for the latter's assistance. In fact, Muhyiddin promised to give the territory of Kimanis to the Sultan of Sulu.

Muhyiddin eventually emerged victorious. Abdul Hakkul Mubin was killed in the civil war and later buried at the royal burial ground on the island. It is not clear to historians whether Muhyiddin asked for Sulu’s help in the civil war. The Sultan of Sulu, however, claimed that he was asked by Brunei to help and was promised eastern Sabah as a reward. The Sultan of Sulu claimed eastern Sabah as a gift from the Sultan of Brunei, for the Tausugs' help during the civil war (an event which traced the roots of the North Borneo dispute between Malaysia and the Philippines in the present-day).