Things Fall Apart, who is responsible for the division and downfall of Umoufia?

In the historical novel Things Fall Apart by Chinua Achebe we gain knowledge of the African societies as they once were. Achebe shows us what happened to this particular (fictional) community in the 19th century, as the downfall of their village occurred.
The book begins by introducing us to the main character, Okonkwo. Okonkwo is a strong character who is a leader in his town of Umuofia. This man has gone through many challenges in his life. It was hard for him growing up with his father Unoka who was "lazy and improvident and was quite incapable of thinking of tomorrow" (Things Fall Apar…