the British involvement in Iraq played a role, and this follows a pattern.
Rwanda for example...
http://www.wsws.org/news/1994/jul1994/rwan-j29.shtml
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German colonialism, followed by Belgian, exacerbated and institutionalised the divisions between the two groups. The Germans attempted to use the Tutsis as colonial administrators, introducing racial theories about their supposed superiority over the Hutus and even their "Aryan" origin.
This system of racial classification had no more basis in science than the master race theories propagated by the Nazis a few decades later. The two groups speak the same language, share the same customs and a common land. Inter-marriage between them is commonplace.
The move toward independence in 1962 did not lift the burden of this legacy of colonialism. Instead independence was accompanied by a campaign on the part of Hutu leaders to settle accounts with the Tutsis. The racist theories of the Germans were adopted, albeit in an inverted form, by sections of the aspiring Hutu bourgeoisie, who attributed a foreign origin to the Tutsis and advocated their expulsion.
When a Hutu-dominated regime came to power in Rwanda, it ran a system resembling apartheid, with "tribal" identity cards and an ethnic quota system limiting the access of Tutsis to schools and government jobs.