As we consider the historical factors relating to the terms Tutsi and Hutu, the terms seems to designate social classes that were established based on an elite conquering group and an indigenous settled farming group.  The arrival of this group, now known as Tutsi, is told in oral traditions of the Rwandan people.  The incoming elite generally associated with the Tutsi seem to have been Cushites from Ethiopia or northern Somalia.

These Cushites were later joined by northern Nilote (Nilotic) nobility who merged into one ruling or elite class.  The name "Hima" seems to be associated with this ruling noble class.  The Bantu-speaking indigenous people are generally thought to have been the original group now identified with the Hutu.  In Rwanda the key references used are the "tall ones" (the Cushite-Nilotic group and the "short ones" (the original Bantu).

Intermarriage
This was somewhat like the feudal setup for centuries in medieval Europe.  Over the centuries, however, at least in the recent historical period, "Hutus" and "Tutsi" have intermarried quite a bit.  This was one of the heart-breaking aspects of the various waves of genocide (of one side against the other, sometimes the Hutus massacring the Tutsis, sometimes the other way around, and sometimes separate patterns of rulership and violence in the two territories or Rwanda and Burundi).

In the colonial period (late 1800s to 1960s), the colonial European powers, first Germany, then Belgium, either created the division or exacerbated it (made it worse) by choosing the "tall ones" (Tutsis) as the ruling administrative class, through whom they ruled indirectly.  This seems to be the more immediate source of the current animosity.  Various scholars who have studied the situation confirm this opinion of the history.

Colonial or Traditional
There are differences of opinion on how separate that identification of Hutu and Tutsi was before the Germans imposed their rule.  Some claim there were no separate "tribes" or ethnicities before the Germans arrived, but this does not seem adequate to explain the historical information available.

Some commentators suggest that "the Germans favored these people because they were lighter in skin color than the oppressed Hutus."  This is consistent with the common racist views in Europe at that time.  However, I have not personally been able to detect much of a difference between the two groups in regard to skin colour. The finer facial features of the Tutsi and their long thin faces seem to be a more prominent distinction.

Several brief commentaries on this questions have been produced in reference to the movie Hotel Rwanda.  Commentators attempt to provide some historical perspective on the problem.  The region had been ruled by Germany as the colony of Rwanda-Urundi.  In World War I, Belgium drove the Germans out of the territories in 1915 (some say 1916).  When Germany lost the war, the territories were taken over by Belgium to be administrated as a League of Nations protectorate.

Formal Distinction
Given administration in 1918, Belgium ran the territories as a colony, though through the local administration of two separate Tutsi monarchies.  It was the Belgians who introduced a racial or ethnic registration distinction in 1926.  The Belgians thus formally classified the inhabitants of their East African territories as two separate "tribes," in the European concept.

How firm these designations already were before the German, then Belgian, formalization of the distinction is still unclear.  Through all this, however, the two "ethnic groups" of Tutsi and Hutu all had the same cultural patterns, language, religion, dances and social culture.  The social structure, however, seems clearly to have already been a class system with ruling Tutsi families on the top tier, and agricultural Hutus as the workers.  Various sources indicate that this feudal structure gradually dispossessed the Hutus of their land by the ruling Mwami (Tutsi king).  This seems to have occurred in the 14th and 15th centuries, thus long before European involvement.

This is a very general sketch of some of the forces at work in the Rwanda-Rundi clashes between the Tutsi-Hutu people/peoples.  Note that thousands of both these groups also live in neighbouring Congo, and that is a major cause of the initial Zairean/Congolese civil war, and the current rebellion (2008) against the central government of the Democratic Republic of the Congo.

Also related:
Anything But Ordinary (Paul Rusesabagina)
The Hima People of Eastern Africa
Hima, Ham and Cush
The Tutsi People – Blog
Tutsi, Hutu and Hima — Cultural Background in Rwanda
Tutsis – the Ethiopia-Somalia Connection

Related on the Internet:
Colonial and Pre-Colonial
Feudalism and Colonialism — Rwanda AfricaGenWeb Project
Review of Hotel Rwanda, Historical Background Second Review of Hotel Rwanda, Historical Background
Tutsi and Chwezi:  History and Pre-History

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