The [Ugandan] army also concentrated on the northwestern corner of Uganda, in what was then West Nile District. Bordering Sudan, West Nile had provided the ethnic base for much of Idi Amin's earlier support and had enjoyed relative prosperity under his rule. Having born the brunt of Amin's anti-Acholi massacres in previous years, Acholi soldiers avenged themselves on inhabitants of Amin's home region, whom they blamed for their losses. In one famous incident in June 1981, Ugandan Army soldiers attacked a Catholic mission where local refugees had sought sanctuary. When the International Committee of the Red Cross (ICRC) reported a subsequent massacre, the government expelled it from Uganda.
...Okello invited former soldiers of Amin's army to reenter Uganda from the Sudanese refugee camps and participate in the civil war on the government side. As mercenaries fresh to the scene, these units fought well, but they were equally interested in looting and did not discriminate between supporters and enemies of the government. The reintroduction of Amin's infamous cohorts was poor international public relations for the Okello government and helped create a new tolerance of Museveni.