Somalia’s thirty years of civil war bear the indelible mark of the region’s former colonial powers, who imposed modern physical and cultural boundaries which became fault lines for conflict. In this respect, the Somali civil war has elements in common with other post-colonial African conflicts that produced mass atrocities in Rwanda, Sudan, the Democratic Republic of Congo and in northern Uganda.
Histories of Somalia are prone to two generalizations: one, that the Somali people have always formed one unified nation that was only recently divided by colonialism; the second, that Somali clan-based violence is a manifestation of an ancient, primordial tribalism. On examination, both accounts are inaccurate.
Spread throughout the Horn of Africa, the Somali people are comprised of numerous clans and sub-clans. Traditionally, Somali society has been marked by nomadic-pastoralism in the north and agricultural pastoralism in the south. Lacking a unitary government, the Somali ‘territory’ was partitioned by the European colonial powers after the late 19th century. Parts of the north were administered as British Somaliland, while much of the South became Italian Somalia. 
There were stark differences in the colonial economic policies of Italy and Britain, which tended to amplify regional traditions. While Italy developed a comprehensive economic plan for the more agrarian southern Somalia, the largely nomadic British Somaliland remained neglected. This situation produced lasting disparities in wealth and infrastructure. Under this colonial economic order, the clans evolved into political identities tied to economic benefits or disadvantages. Rivalry was inevitable, particularly once the end of colonialism produced the first unified Somali state. 
A Post-Colonial Experiment: 1960-1969
In 1960, the southern Italian Somalia and northern British Somaliland merged to form the Somali Republic. In the new political order, the south obtained de facto hegemony over the underdeveloped north. These regional rivalries had a broad impact on clan politics. The prestigious Isaaq clan—once the majority in Somaliland— became a national minority. The Darood clan— once a minor player in the north— rejoined Darood from the south to form a powerful new entity. Tension between the clans meant a fractious parliamentary system, as the clans aligned themselves with competing political parties. 
Despite the contentious clan relations, the 1960-1969 Somali Republic was considered a model post-colonial state. Political participation outpaced many Western democracies. Suffrage was extended to women in 1963. All this ended in 1969, when a bodyguard assassinated President Sharmarke and the army intervened and seized power. 
Major General Siad Barre became the head of a military regime aligned with the Soviet Union and espousing the principles of ‘Scientific Socialism’ and expansionist Somali nationalism. Under Barre’s rule, the military regime would attempt to impose a monolithic centralized state on a Somali civil society that had never formed a single homogeneous nation-state. This unstable political form—maintained only through violence—would prove to be a pressure cooker for conflict. 
 “The heritage of war and state collapse in Somalia and Somaliland: local-level effects, external interventions and reconstruction” [PDF], Ismail I. Ahmed and Reginald Herbold Green, Third World Quarterly, 1999.
 Somalia: A Country Study. Helen Chapin Metz, ed. Washington: GPO for the Library of Congress, 1992, accessed August 10, 2009.