Like any great novel, Things Fall Apart develops multiple themes, including (according to the Enotes study guide):
- Custom and Tradition
- Choices and Consequences
- Alienation and Loneliness
- Change and Transformation
- Good and Evil
- Culture Clash
All of these themes are interrelated, but I think the two most important ones are "Custom and Tradition" and "Culture Clash." The novel is broken up into three sections: the first two sections focus on the customs and traditions (Week of Peace, isa-ifi ceremony, Feast of the New Yam) of the Ibo tribe before the colonization. The last third of the novel focuses on the culture clash between the African and British systems.
These customs and traditions establish the Ibo culture as communal (they share resources), agrarian (they rely on farming), polygamous (the men have many wives), polytheistic (believe in many gods, animistic (attribution of "souls" to plants, animals) oral (they pass on stories), integrated (they have no separate institutions), and patriarchal (male-dominated). The customs and traditions protect the tribe and help it survive. The Ibo's cultures and traditions have allowed them to survive in the harsh climate for centuries. But, Achebe does not idealize the culture: he shows how the Ibo are distrustful of outsiders; they fear war; they are superstious; they have segregated gender roles. All of these customs and traditions are themes developed by Achebe to revive his African past and to set up how they are about to be transformed by the customs, traditions, religion, and technology of the white man in the last section of the novel.
The "Culture Clash" theme of the last third of the novel reveals how the white man's (British) customs and traditions clash with the Ibo's. The British establish their culture as invididualistic (do not share resources), industrial (rely on technological production), monotheistic (believe in one God); Christian (believe in Christ as savior); print-literate (use writing, paperwork); and have integrated gender roles (men and women share same roles). Above all, though, the British are institutional: they have schools, legal system, prisons, and other facilities for their beurocracies. So, the Ibo culture begins to "fall apart" as they adopt some of these British customs and traditions. Their culture begins slowly to transform and unravel. Okonkwo, the symbolic figure of the Ibo culture, kills and is killed, revealing that these two cultures cannot co-exist in Africa.