Essentially, the impact of colonization is to break apart the Ibo societal structure. In some ways, this has negative effects: traditions are destroyed, and those who follow Ibo law are suddenly subject to British punishment. Many villagers die or remain in jail because of their adherence to their own rituals and traditions, rather than the recently imposed British structure. Religious conflict is brutal, and both villagers and missionaries die because of their inability to adapt to change. Okonkwo demonstrates the worst that could happen to someone who is unable to transform when history forces change. His aggressive stance toward the missionaries brings about his own destruction.
There are some positive effects of this interaction however. The Christian missionaries bring a kindness and acceptance that many villagers do not know. The practices of leaving twins to die, or turning out "undesirables" are abhorred by the the missionaries, and many women and disenfranchised members of the tribe find a place within the structure of the church.
Chinua Achebe's Things Fall Apart, is a novel about Nigeria in the 19th century before colonialism. It is a tale about a great westler and elder. Itis not until the novel's end that the reader learns about colonialism.This novel is really a display of one author's opinion of what happens when colonialism enters a culture--things fall apart. The tale is really Okonkwo's story and shows how he became well known however he was stubborn which was always a problem. As a result, a stray bullet from his gun fatally killed someone. He was exiled, along with his family, for 7 years. When he returned everything had changed.
This is a common occurance in countries where colonialism takes over the culture; people return to their homeland to find out that they no longer recognize the place and they are no longer accepted there. (See the Inheritance of Loss in Enotes which also related to colonialism in India)
The land changed, the people were no longer the same. Some people accepted the new fate and no longer did things the traditional way. Before the colonists came the land was known for believing that twins were evil, which was the main reason they were left in the evil forest but after the colonists came twins were no longer thrown away, the church took them from the evil forest instead and raised them. Okonkwo was no longer seen as the man he once was, the traditional man no longer meant anything, and those who were unable to move along with the changes or accept them, usually suffered a great deal such as okonkwo and killed themselves.