First, to get the caveat out of the way: any attempt to generalize an 'Africa' across 55 countries, over a billion people, and thousands of communities of language and culture subtending the second largest continent on Earth, is going to be a Western stereotype in the sense that we feel OK generalizing it at all. The Western press (and to some extent, even African news organizations) is generally complicit in this by giving column inches to only certain types of stories; you hear about tribalism in X or Y place but obviously you don't hear about it where it's not a major line of socioeconomic fracture.

With that out of the way: no, Africa is not uniquely susceptible to tribalism in any innate way. To understand the modern phenomenon of tribalism--which is almost always characterized as a primitivist holdover from inferior 'stages' of civilization even though we've jettisoned that model of understanding human societies--one must consider the process of tribalization that took place, wittingly and unwittingly, in the colonial and postcolonial eras.

First, the process of tribalization was part of the drive to rationalize human societies that grew out of the Enlightenment and informed travelers from Europe to Africa, including missionaries; when the colonialists arrived, they were informed by those accounts, and built upon them. The idea that African 'tribes' were ahistorical, largely timeless entities that had some essential characters is very much a part of 19th-century racial science. (Terence Ranger's two essays on the invention of tradition in Africa, and Leroy Vail's introduction to The Creation of Tribalism in Southern Africa (1990), are essential reading here.) So in terms of 'native' authorities, administration, reorganization, and so on, colonial powers taking on authority in African settings tended to look upon identity groups as tribal. The fluidity of some of these identities, the ability of individuals to layer multiple descriptors and languages, and the tendency of such things to pop in and out of being depending on particular formations of society and authority, were frustrating and opaque to colonial rationality. It was easier to reify such groups in their current states, and fit with the worldview, even though individual officers interacting with people often spotted the incongruity. Such 'grouping' could also work as a mode of rule itself, as in divide-and-rule tactics that were not unique on the African continent.

But that's only part of the story. Thomas Spear's 2004 essay on neo-traditionalism and the limits of invention (in the Journal of African History) points out that these identities were never created whole-cloth or changed pell-mell. Virtually every 'tribal' division that colonial authority recognized had a precolonial past; whether or not it was a complete misunderstanding to impart certain meanings or characteristics to a linguistic, cultural, or political identification could vary greatly. People also needed to have a reason to accept the reification of an affiliation into a 'tribe,' and sometimes even saw the opportunity to use 'tribal' affiliations as a mode of collective resistance and/or diminution of vulnerability to colonial extraction for themselves and their families (as in the case of Zulu identity, in part, per Michael Mahoney's The Other Zulus). Rulers over loose identity clusters often took the guarantee of hereditary privilege colonial schemas offered them, and if they wouldn't, someone else might, as in the warrant chief schemes the British tried to build in SE Nigeria or southern Rhodesia (Zimbabwe). These divisions often became ones that dictated privilege, access to government, resources, and the like, which carried into the postcolonial era in exceptionally potent ways for some nations. It's important to note that the divisions already existed in some way--to varying degrees of permeability--but colonial rule hardened a lot of them out of misunderstanding or for reasons of functionality. The Belgians with the Hutu and Tutsi in Ruanda-Urundi are a classic case; they supported the 'more European' Tutsi ascendancy and defined them in an essential, permanent way [edit: where before flexibility and crossings between groups were possible], only to shift support to the Hutu when that ascendancy began to oppose them in the 1950s (the first Rwandan genocide). The division, again, was real, but its character changed under colonial rule--whether for benefit or as unity in opposition.

Postcolonial regimes either have internalized these identities or have found the de facto mode of rule by tax-farming and 'traditional authorities' that the colonial powers used to be the most economical or efficacious. Thus, in many cases, these divisions and their modified characteristics persist except where efforts exist to try to subsume them (and perhaps even there). If one looks at Kenya versus neighboring Tanzania, for example, a difference in the strength and character of tribalism is instantly apparent. That is one part the result of a different set of priorities for the ruling powers, and one part a dedicated nation-building project (language, education, commonwealth) under Julius Nyerere from 1961 to 1980 which had many material failures but did enjoy that particular success. Other cases, like Botswana or Lesotho, are based on single kingdoms recreated into unified identities; tribalism in Ghana, where the pan-African project had a strong intellectual foothold as in mainland Tanzania, is also quite muted, and in wide swaths of the former French colonies of Africa, the mode and strength of tribalism vary depending on a very long history. The grouping together of Africa, and blaming tribalism in a generalizing, hand-waving way as a major source of 'Africa's' economic ills, is absolutely Western; it looks at the symptoms within the feedback loop, and concludes that they are the cause. One must see what tribalism overlays in the past as well as the present to get any real explanatory value out of the imputation. Where significant tribalism exists, it is certainly a significant problem, but it isn't just some holdover from an unchanging past.

[edit: The other question, "how much of a problem is it, really," is within the 20-year embargo of this sub, so that's one for the political scientists / anthro types.]