This is a very pertinent question to consider. What you need to remember is that Achebe, as an African author, is clearly not going to present his own African countrymen as being uncivilised. On the contrary, what he does is to present us with African culture before the white European colonialists arrived in order to explode this myth and to present African culture to us in all of its richness and complexity.
One argument for suggesting that the Ibo culture is uncivlized would be the way that they have various taboos against such groups of people as twins and other outcasts of society. These are of course among the first converts to join Christianity because of the way that they are able to rise in status and importance in European culture. However, we must be very careful in the way we read such information, for Achebe is clear to describe European culture as a culture that gives more prestige to some than to others. Ibo culture is not therefore presented as being "uncivilized," it is just presented as being a culture like any other, which, in spite of its differences to European culture, is similar in the way that it gives status and prestige to some and makes others outcasts.