This novel is full of examples of power and oppression, both from the colonial incomers to the power of tribal chiefs trying to maintain their position. However, one theme of the book which will help you examine the concepts of power and oppression more clearly is that of change vs tradition.
This novel is really the story of a village and a culture on the edge of change and the two forces of change and tradition are often pitted against each other. It is noteworthy how characters react differently to this dilemma. Okonkow, for example, is against the forces of change, but we can see that he fears he will lose his status that the traditional society gives him. He fears that these new ways are not manyly and that by following them he will be made unmanly too. Yet conversely, the outcasts of his society rush to embrace Christianity precisely because of the societal status that it gives them - a good example of the power and oppression within the society before colonialism. It is interesting therefore to examin the character of Okonkow in this context, as although he wields power he can also be said to be oppressed by it as he is trapped into his position, which arguably leads to his tragic ending.