According to obierika, the clan could easily drive out two white men. why then, does he feel the clan is falling apart?

he feels the clan is falling apart because of those who are converting to Christianity and putting aside tribal practices. He also acknowledges the unwillingness of their people to fight the white men.

This gave white men competitive advantage towards his clan on top of their already more modern weaponaries, which leed to the downfal and many deaths of his Tribes members