Death

Death is really the main instigator in the novel.
Okonkwo 'slay's the cat'. In this case, I'm classifying it as dying, because the fighting represents killing people. He sees that he can be strong and earn hponor for causing death, and this really what starts his fasination in death, or having control over others.
When Okonkwo's dad dies, he sets out on his own, trying to become everything his father was not. He creates his own little empire of wives, kids, and yams. He honors and feels he should be honored for killing men in war, for having heads in his house, to drink out of.
Okonkwo lives this life of honor, until he kills his for-all-intents-and-purposes son. His death really symbolizes the first real signs of emotion in Okonkwo.
The next time death changes things is when Okonkwo shoots the man at the party. It sends him to his mother's land. The church resides on the land of the evil dead, and takes in those who are sick. When Okonkwo returns to his homeland, he ends up killing himself over the total take over of the church, and the towns reluctance to kill all the church members.