They are directly related to the poem as events are taking place.
The words of Yeats influenced Achebe. Things Fall Apart closely shows the idea of anarchy being loosed upon a world. "A knife was put on the things that held us together and we have fallen apart," wrote Achebe (Things Fall Apart 176). This quote can directly be taken to the idea of "things" falling apart for the Ibos; their clan separated and these rifts came to Okonkwo, as his son fell away from the family to become a Christian. "The centre cannot hold" is another important phrase, in "The Second Coming," which relates to Things Fall Apart. Achebe wrote, "The white man came quietly and peaceably with his religion" (Achebe 176). The Christians came in peacefully to establish a mission to bring religion and convert the "uncivilized" Ibos. However, their peaceful mission causes trouble for the Ibos. "The falcon cannot hear the falconer" is linked to the converted who no longer heard the ideas of their traditions and traditional culture and beliefs. "Now the white man has won our brothers, and our clan can no longer act like one," said Achebe (176). The white men proved to be the "anarchy loosed" upon the Ibos as they caused many Ibos to fall away from "the centre." Enoch's action of unmasking the egwugwu instigates battle between the Ibos and the church. The unmasking also connects to the assassination of the Archduke because that caused the outbreak of a war in Europe, and the unmasking of the egwugwu caused the outbreak of hostilities between Ibos and the Christians.
The colonial connection is not however, the only interpreted connection between "The Second Coming" and Things Fall Apart. One can also make the argument that Achebe is writing a response to the idea in the poem that the world will be swept by a tide of savagery from the uncivilized portions of the globe. Achebe himself says, "I would be quite satisfied if my novels (especially the ones I set in the past) did no more than teach my readers that their past with all its imperfections was not one long night of savagery from which the first Europeans acting on God's behalf delivered them" (Achebe 20).