So why, then Americans or Africans did not come to Europe to conquer, enslave and exploit, but the other way around? Does the fact that Europeans already possessed technology and institutions that gave them superiority over others _before_ they landed in America or Africa have anything to do with it?
We can ask what conditions give Europeans that superiority, but assuming that it was benefits of future exploitation defies the most rudimentary rules of logic. My preferred response to this question is "geographical accident" - the geographical location of Europe gave it the advantage of exchanging agricultural technologies with other peoples across the Eurasian land mass because most of that land mass was in the temperate climate zone, which made the agricultural technology dissemination possible, Ag technological advances, in turn, produced surplus, freeing parts of population to engage in pursuits other than food production, which further aided creation of new technologies, including military technology.
Both African and American land masses, by contrast, are spread through several very different climate zones, which effectively inhibited agric. technology dissemination. As a result, technology advances on these continents were confined to small geographical areas and did not benefit from exchange with other peoples. This argument was advanced by Jared Diamond in _Guns, germs, and Steel_.
In short, Europeans dominated because they were lucky to find themselves in a resource rich- and favourable geographical environment. If the Africans or Americans found themselves in a similar geographical environment, it would be them who landed on different continents, colonized, enslaved, and plundered.
As far as slavery is concerned - this institution was brought to Africa by Arab traders and practiced for centuries. Americans took advantage of it, but Europeans did not for obvious reason. Europeans did not face a shortage of cheap indentured labor, the Americans did. However, it is European colonialism that finally ended the slave trading practices in Africa. European colonization of Africa (but not South Africa!), terrible as it was, actually brought progress by ending the Arab slave trade and introducing Western institutions and technologies.
Wojtek