One aim of a revision here will be to create a statement that is at once broad enough to encompass the entire argument you will pursue in your essay and also specific enough to communicate the essential point that anchors the essay's argument.
Manipulating others for selfish reasons will inevitably lead to negative consequences.
We will want to tie this idea to the novel directly if we can and begin to present some of the points of evidence that you will use to support the argument.
Is the focus of your essay on the character of Okonkwo and his tendency to rule his household according to self-interest (so that he will be seen as strong, manly and successful)? If this is the case, you may want to indicate Okonkwo in your thesis statement.
The notion that Okonkwo's behavior can be described as creating and sustaining a cycle of fear is certainly present in the text.
"Okonkwo ruled his household with a heavy hand. His wives, especially the youngest, lived in perpetual fear of his fiery temper and so did his little children. Perhaps down in his heart Okonkwo was not a cruel man. But his whole life was dominated by fear, the fear of failure and of weakness."
Okonkwo's temperamental behavior, which often manifests as harsh treatment of others, is thus suggested to be a negative aspect of his character and is connected to a cycle akin to the one suggested in your current thesis.
If your focus will be on the English who use certain specific weaknesses of the Igbo social system (i.e., its most strident and exclusionary practices) to undermine the stronger elements of the social system (i.e., the Igbo sense of social continuity and cultural identity), we will want to build that into the thesis statement as well if we can.
Working in this direction, your thesis argument would attempt to deal with these ideas explicitly: The self-interest of individuals and social groups that leads to manipulative behavior in Things Fall Apart suggests a negative cycle with inevitable consequences. Okonkwo's treatment of his family parallels the manipulative behavior of the English colonists in the novel and each contributes to a thematic question regarding integrity and moral strength.
Finally, a note on grammar: Be careful to avoid pronoun disagreement.
Universal Idea: manipulating others leads to consequences especially if one is engulfed by their selfish mindset.
In the current version of your thesis, the term "one" is in disagreement with the possessive pronoun "their." A variety of alternatives have been presented above, but if you were to simply adjust this statement we would want to replace "their" with "a," "his," "her," or "his or her." Other revisions would work equally well, such as adjusting "their selfish mindset" to "selfish interests" or "self-interest."