Imperialism, put simply, is a policy whereby a country extends its power and influence either by diplomatic means, military intervention or some other stratagem. Things Fall Apart acts as a counter narrative to imperialism in that it exposes the flaws inherent in such a policy.
In the novel, we are introduced to the cultural, religious, legal and economic traditions of the Ibo people. These traditions had become entrenched and were a way of life for them. Members of the tribe unquestionably accepted authority and and everyone knew his place and enjoyed the freedoms and privileges offered by such an existence. In effect, members were happy with what they had and their lives were, although not idyllic, satisfying.
The arrival of the British imperialists gradually eroded the cohesion within Ibo society. They introduced a new religion, new laws and a new government. Once the Ibo were exposed to these new conditions, conflict ensued. The imperialists, through their new laws, dealt out harsh punishments to those who opposed them.
The imperialists' religious doctrines and values were in direct contrast to those practiced by the Ibo, and many Ibo questioned their own belief system and turned to the new church. This created conflict between members of the Ibo since many of them, such as the protagonist Okonkwo, perceived the dangers posed by the imperialist system. He believed that its influence would eventually lead to the destruction of their traditional way of life.
Okonkwo's death is symbolic of the death of Ibo culture. The growth in the imperialists' influence is contrasted by the decay of Ibo culture. Many Ibo began to resent the strictures of their own culture and rebelled against it by adopting the new system of thought. The obvious outcome was that centuries of tradition became nothing. The conventions introduced by the imperialists were harshly enforced and became like a greedy monster swallowing everything in its path until almost nothing was left.
In the end, the novel clearly depicts the destructive nature of imperialism. It is a system of oppression which has no respect for the beliefs and cultures of those upon whom it imposes itself. It disintegrates and eventually destroys traditionally functional societies. Those who become its victims are left with no choice but to adapt, face incarceration and torture, or die. Such is the tragedy of Things Fall Apart.