Chinua Achebe's first three novels are sometimes called "The African Trilogy." They are Things Fall Apart (1958), No Longer At Ease (1960) and Arrow of God (1964). I read Things Fall Apart (probably the most widely read African novel) some time ago, I have not read No Longer At Ease. Most of Achebe's writing (and he has published a great deal of work) deals with the impact of the British colonization of the Igbo lands of northern Nigeria on traditional culture there and particularly with the loss of authority of African priests under pressure both political and religious. Both Things Fall Apart and Arrow of God present tragic protagonists who embody this authority, and in both books the human weaknesses and character failings of these men are presented as important elements contributing to societal collapse. This discussion of African weaknesses in confronting colonization, always in microcosm, is key to Achebe's success in illuminating the catastrophic 20th century history of the region: it is intellectually fruitful, provocative, and gives Achebe moral authority both in Nigeria and in the outside world (I was surprised to discover that Achebe, 81 this year, continues working as a member of the faculty at Brown University).
Arrow of God is denser with detail than Things Fall Apart, with a good deal more technical discussion of the rituals and concepts underlying Igbo religious customs and with a larger and more fleshed-out cast of characters. Ezeulu, priest of Ulu, the titular deity of a small and remote group of villages, nobly resists cooptation by the heavy-handed and not particularly competent British authorities. He is secure in his own identity and standing, a believer in his own authority and function. This gives him the instincts needed to resist usurpation but also clouds his ability to recognize that his tradition is under genuine threat. He commits two errors, first by sending one of his sons, Oduche, to become a Christian (Ezeulu sees this move as essentially strategic) and second by refusing to perform the ceremony needed to authorize the yam harvest while he is detained by the British, two overreaches that have disastrous consequences.
Achebe, who never patronizes his own culture, shows how rival priests (each with their own deity) function as political agents (what appear to be religious contests of magic have roots in disputes over farmland), and have shallower roots than their rhetoric implies (the religious disposition of Ulu goes back, not to the beginning of time, but to organizing against African slavers decades before). A cultural system, like an ecosystem, is deceptively fragile. Thus Achebe wields a double-edged sword: Britain is called to account for its immensely destructive imperial policies, but Africans are confronted with their own guilt for failing to criticize themselves and adapt to modern challenges.
Two contemporary Nigerian novels that each, in different ways, continue Achebe's examination of cultural erosion and that have been the subjects of posts here are Ben Okri's The Famished Road (1991) and Chimamanda Ngozi Adichie's Purple Hibiscus (2003).