The first group to initiate hostilities were the Amin loyalists who launched a rebellion against the UNLF government in the autumn of 1980.
Their 7,100-strong force never adopted an official name, but is generally called "Uganda Army" as it consisted for the most part of old troops of Amin's Uganda Army (it was also known as "West Front" or "Western Nile Front").
The rebels were not truly unified but split into several bands that were loyal to numerous officers who had previously served under Amin such as Emilio Mondo, Isaac Lumago, Isaac Maliyamungu, Elly Hassan, Christopher Mawadri, and Moses Ali.
Amin arranged for the group to receive money from Saudi Arabia in preparation for a large-scale attack across the border against the West Nile sub-region.
On 6 October, one week before the offensive was to commence, about 500 rebels crossed the border and attacked the town of Koboko.
The 200-strong UNLA garrison was on parade at the time and was unarmed; the rebels massacred the soldiers.
Word of the attack spread to other UNLA garrisons in West Nile, who quickly fled to the Nile River, leaving the Uganda Army's advance unopposed.
They were welcomed by the local population, which had tense relations with the UNLA.
As the rebels knew that they could not hold the captured territory against a full UNLA counter-offensive, they mostly retreated back into Sudan after a few days with a large amount of loot.
The UNLA began its counterattack on 12 October accompanied by Tanzanian forces.
The only significant resistance they encountered was in Bondo, where six Tanzanians were killed.
The UNLA forces, considering the local population hostile, engaged in a campaign of destruction and looting across the West Nile, as Tanzanian officers tried in vain to restrain them.
They leveled the town of Arua, killed over 1,000 civilians, and provoked the flight of over 250,000 refugees to Sudan and Zaire.
The brutality of the UNLA inspired further unrest, as peasants and ex-soldiers took up arms to defend their lands from the government forces.

The Uganda Army launched its next offensive just before the Ugandan national elections in December 1980.
In one of their most daring actions, the rebels ambushed Obote as he was touring the West Nile region.
They almost killed him and Tito Okello, a high-ranking UNLA commander.
This time, the Uganda Army also held the areas it captured in West Nile, and set up a parallel government after retaking Koboko.
After about one month of combat, the insurgents had captured most of West Nile, leaving only some towns under UNLA control.
However, many rebels focused more on looting the area and taking the plunder back to Zaire and Sudan than on fighting the UNLA.

The West Nile rebellion was weakened by internal divisions as parts of the Uganda Army remained loyal to Idi Amin, whereas others wanted to distance themselves from the unpopular old dictator.
The latter part of the insurgent army split off, forming the "Uganda National Rescue Front" (UNRF) under Moses Ali, whereas the remaining Amin loyalists were still called the "Ugandan Army" until becoming known as "Former Uganda National Army" (FUNA).
The West Nile rebels soon started to fight each other.

Furthermore, southwestern Uganda experienced a resurgence of the Rwenzururu movement which wanted self-determination for the Konjo and Amba peoples.
The movement had been largely dormant since the 1960s, but managed to take control of weapon stockpiles that had been left unguarded when Amin's government collapsed in 1979.
They thus resumed their insurgency, and the security situation in the mountainous border areas of the southwest quickly deteriorated in 1980.

Meanwhile, the UNLF government experienced its own divisions.
As the UNLA was being transformed from a loose alliance of various anti-Amin insurgent groups into a regular army, the different political factions attempted to ensure that their own loyalists would be present and dominant in the new military.
Obote outmaneuvered his rivals, most importantly Yoweri Museveni, and made his 5,000-strong Kikosi Maalum group
The first group to initiate hostilities were the Amin loyalists who launched a rebellion against the UNLF government in the autumn of 1980. Their 7,100-strong force never adopted an official name, but is generally called "Uganda Army" as it consisted for the most part of old troops of Amin's Uganda Army (it was also known as "West Front" or "Western Nile Front"). The rebels were not truly unified but split into several bands that were loyal to numerous officers who had previously served under Amin such as Emilio Mondo, Isaac Lumago, Isaac Maliyamungu, Elly Hassan, Christopher Mawadri, and Moses Ali. Amin arranged for the group to receive money from Saudi Arabia in preparation for a large-scale attack across the border against the West Nile sub-region. On 6 October, one week before the offensive was to commence, about 500 rebels crossed the border and attacked the town of Koboko. The 200-strong UNLA garrison was on parade at the time and was unarmed; the rebels massacred the soldiers. Word of the attack spread to other UNLA garrisons in West Nile, who quickly fled to the Nile River, leaving the Uganda Army's advance unopposed. They were welcomed by the local population, which had tense relations with the UNLA. As the rebels knew that they could not hold the captured territory against a full UNLA counter-offensive, they mostly retreated back into Sudan after a few days with a large amount of loot. The UNLA began its counterattack on 12 October accompanied by Tanzanian forces. The only significant resistance they encountered was in Bondo, where six Tanzanians were killed. The UNLA forces, considering the local population hostile, engaged in a campaign of destruction and looting across the West Nile, as Tanzanian officers tried in vain to restrain them. They leveled the town of Arua, killed over 1,000 civilians, and provoked the flight of over 250,000 refugees to Sudan and Zaire. The brutality of the UNLA inspired further unrest, as peasants and ex-soldiers took up arms to defend their lands from the government forces.
The Uganda Army launched its next offensive just before the Ugandan national elections in December 1980. In one of their most daring actions, the rebels ambushed Obote as he was touring the West Nile region. They almost killed him and Tito Okello, a high-ranking UNLA commander. This time, the Uganda Army also held the areas it captured in West Nile, and set up a parallel government after retaking Koboko. After about one month of combat, the insurgents had captured most of West Nile, leaving only some towns under UNLA control. However, many rebels focused more on looting the area and taking the plunder back to Zaire and Sudan than on fighting the UNLA. 
The West Nile rebellion was weakened by internal divisions as parts of the Uganda Army remained loyal to Idi Amin, whereas others wanted to distance themselves from the unpopular old dictator. The latter part of the insurgent army split off, forming the "Uganda National Rescue Front" (UNRF) under Moses Ali, whereas the remaining Amin loyalists were still called the "Ugandan Army" until becoming known as "Former Uganda National Army" (FUNA). The West Nile rebels soon started to fight each other.
Furthermore, southwestern Uganda experienced a resurgence of the Rwenzururu movement which wanted self-determination for the Konjo and Amba peoples. The movement had been largely dormant since the 1960s, but managed to take control of weapon stockpiles that had been left unguarded when Amin's government collapsed in 1979. They thus resumed their insurgency, and the security situation in the mountainous border areas of the southwest quickly deteriorated in 1980.
Meanwhile, the UNLF government experienced its own divisions. As the UNLA was being transformed from a loose alliance of various anti-Amin insurgent groups into a regular army, the different political factions attempted to ensure that their own loyalists would be present and dominant in the new military. Obote outmaneuvered his rivals, most importantly Yoweri Museveni, and made his 5,000-strong Kikosi Maalum group 
Ugandan Bush War