things fall apart on racist

I assume you mean on "racism." If that's the case, then there are several ways I would suggest approaching this essay. The first is to compare the different white figures who come to visit the clan. Mr. Smith, Mr. Brown and the District Commissioner all have different views of the tribe based on different assumptions of their "savagery" and their actions reflect this. A compare/contrast essay would be pretty straightforward. Another way to approach racism would be to compare the way the missionaries/colonists judge the Africans in the tribe with the way that those within the tribe (mainly Okonkwo) judge one another. Okonkwo has his own prejudices - towards weakness, things he identifies as womanish, towards music - and he is harsh about those. Asking the question of what makes the racism of colonists different from the other prejudices within the tribe could be an interesting essay as well.