THE Soviet Union is breaking up. So is Yugoslavia. Can Africa, and the remainder of the developing world, be far behind?Just as the Soviet Union's internal empire consists of ethnic groups and nationalities cobbled together without regard to history or, in some cases, to original geography, so today's independent Africa is a remnant of the empires of Europe. Most of the countries of Africa can claim no legitimacy other than their accidental origin, usually in colonial or immediately precolonial times. Only tiny Swaziland and Lesotho are ethnically homogeneous, although Botswana almost joins them. Somalia, which nominally is the home of a single people and a single language, is riven by clan rivalries and a true civil war. When the occupying powers of Europe arrived in the 19th century, they found a few large indigenous empires, like those based on the Fulani conquest of what is now northern Nigeria or the Zulu conquest of much of southeastern Africa. For the most part, the ambitions and rivalries of Europe sundered those comparatively recent territorial amalgams. Britain, France, Belgium, Portugal, Germany, Spain, and Italy bundled the peoples of Africa between borders with little respect for any internal coherence. Colonial and modern Zambia, for example, includes 70 peoples, many of whom have been separated from their fellow tribesmen across what are now national borders. Giant Zaire spreads across several geographical and climatic zones and includes peoples of the city, the only true jungle in Africa, the savannah, and much else. Even smaller nations like Kenya and Uganda encompass persons as different ethnically and linguistically as Ukrainians and Kazakhs, or Tatars and Georgians. From its inception three decades ago, the Organization of African Unity (OAU) pledged itself to retain the meaning of the third word in its title. Its charter enshrined an absolute ban on altering national borders, no matter how originally illegitimate or divisive of peoples. The OAU leaders knew they had inherited fragile and questionable borders. Unchecked irredentism would therefore undermine the peaceful development of black Africa and lead to wars that would loosen the already weak glue holding the former colonial territories together. The rulers of Africa understood then and know now that republicanism on the Balkan model would destroy their mostly poor and struggling countries. Even today, few have achieved more than nominal nationhood. The possibilities for fracture and inter-ethnic dispute remain. NIGERIA, the most populous of African nations with about 150 million people, is almost always on the verge of being pulled apart by centripetal forces. Muslims and Christians, northerners and southerners, educated and uneducated vie for what's left of the spoils of oil and the national purse. The Sudan is Africa's largest land in terms of square miles. It yokes together Muslims, Christians, and animists, desert and deep forest dwellers, slavers and ex-slaves, and long-time rulers and their subjects. When the dark-skinned Africans in the south revolted against their lighter-skinned Arab overlords more than a decade ago, control over newly discovered oil deposits was the precipitating factor. The Sudan could, and perhaps should, fall apart. So might the incompatible parts of Nigeria, Zaire, Chad, Tanzania (with its Zanzibar and Pemba), Niger, Senegal (and Casamance), Uganda, and so on. An irredentist or republican case might be made for the ethnic purity of parts of each of those wholes, and many more. Even South Africa has its regional as well as its minority-majority disparities. But except in a very few special cases, the countries of Africa will remain whole. Even if they struggle for another decade or more to establish their nationhood from a congeries of peoples and languages, they aren't likely to go the way of the Balkans or the Soviet Union. Most of the possible divisions can claim too few indigenous resources. Few potential break-away republics, moreover, have much of a history of a separate economic or political existence. Eritrea was governed separately by the Italians for about 70 years, which is the basis for the independence from Ethiopia it now seems likely to achieve. But the Eritrean case supports the supposition that the nations of Africa will stay together. Indeed, Tigre, with a less defined prior history of autonomy, will probably remain part of mother Ethiopia (itself a 19th-century indigenous imperial creation). In black Africa and South Africa, the center is almost certain to hold. The fission of contemporary eastern Europe will not spread to Africa or to the remainder of the developing world. The peripheries, in most individual cases, are simply too weak and too unsure of themselves.