Archaeological and linguistic evidence suggests that from early in the Christian era, Acholi was settled mainly by Central Sudanic (or "proto-Central Sudanic") speakers in the west and Eastern Nilotic ("proto-Eastern Nilotic") speakers in the east. Before the late seventeenth century, Luo speakers were limited to only a few peripheral areas of Acholi. All of these early inhabitants were ironworking mixed farmers, organized into localized patrilineal lineages or, in some cases, into temporary groupings of two to four such lineages.
A new sociopolitical order—and the basis of an Acholi identity—was established when chiefly institutions and ideology were introduced into Acholi by Luo-speaking Paluo from the neighboring kingdom of Bunyoro-Kitara. Central to the new order were a set of notions about political leadership in which chiefs ( rwodi; sing, rwot ) shared power and decision making with the heads of chiefdoms' constituent lineages; a system of redistributive tribute within each polity, with the chief at the center; and royal, often rainmaking, drums as symbols of sovereignty and authority. Over the late seventeenth and eighteenth centuries, some seventy chiefdoms were founded throughout the area that became Acholi, leading to the development of a new social order and political culture, the spread of a new language (Luo), and the evolution of a new society and collective identity. This complex process was helped along by two major droughts, probably during the 1720s and c. 1790, which promoted larger-scale political leadership that held the promise of greater stability and security, and by the formation of neighboring identities against which members of an emergent Acholi could compete, compare, and define themselves.
Over the second half of the nineteenth century, Acholi was incorporated into international trade networks through the activities of northern, Arabic-speaking ivory and slave traders. This trade brought new wealth into Acholi that was unevenly accumulated, with rwodi and interpreters (and eventually their sons and other kinsmen) the major beneficiaries. The northerners also contributed to the further evolution of an Acholi identity, not only by introducing the name "Shuuli," which eventually became "Acholi," but by acting in ways that promoted Acholi as a meaningful ethnic and geographic entity.
When Britain established its rule during the early twentieth century, both ideological predisposition and practical utility prompted the colonizers to consider the Acholi a "tribe" and to administer the area as a "tribal" unit. From the beginning, the Acholi were marginal compared to Britain's concern with Buganda, at the core of the colony. Acholi's role in the colonial economy was confined mainly to the peasant production of cotton as a cash crop and the provision of recruits for the colonial army or police and migrant labor for the more "developed" Buganda. Both Protestant and Catholic missionaries were active in Acholi from early colonial rule, providing written Luo religious, educational, and historical texts and producing a local educated elite, all of which fostered the further development of an Acholi identity within the colonial context of "tribal" culture, consciousness, and politics.
With independence, the Acholi remained marginal within the framework of Uganda as a whole, with one crucial exception: their disproportionate numbers in the police and army. Comprising less than 5 percent of the country's population, during the early years of independence the Acholi constituted more than 15 percent of the police force and fully a third of the army. This special access to Uganda's security forces has alternately presented opportunity and danger as a succession of regimes replaced one another in a cycle of political violence often played out in ethnic (or "tribal") terms. In the most recent phase of the cycle, beginning in the mid-1980s, Acholi has largely been on the receiving end of the violence. Uganda's current army, various local rebel groups (some headed by apocalyptic "prophets" such as Alice Lakwena), and heavily armed Karamojong raiders have all raped, looted, killed, and destroyed, making any kind of normal life in Acholi impossible.