In "Marriage is a Private Affair", what is the Okeke's external conflict?

The fundamental external conflict that Okeke has is that
he cannot accept the marriage of his son.  In his mind, Nene is an unacceptable choice
for a couple of reasons. The first is that she is of a different cultural background,
not of the Ibo of which he and his son are a part.  Additionally, Okeke did not choose
Nene for his son.  He selected someone else for his son, a neighbor's daughter who "has
studied in a convent," and who seems to be a more acceptable choice to his liking. 
Finally, the fact that Nnaemeka chose a wife on his own, without consulting Okeke
represents the last reason that his external conflict is so pronounced.  He sees his
son's actions in a variety of ways, with all of them being bad and representing a form
of disenchantment and resentment with his son.  The external conflict reaches its zenith
when the son sends Okeke a wedding picture and it is returned with Nene's likeness
marked up and hacked up with what appears to be scissors or a razor.  The external
conflict is defined as son and his life versus the father and his own expectations. The
ending with Nene's letter is what brings resolution to this external conflict,
transforming it into a physical one.  The father's anger melts at the mention of his son
and grandsons, and turns into fear that he will not have time to right his wrong.  It is
here where Achebe might be trying to use the situation to represent a "teachable
moment."  External conflicts over something small have a tendency to fester over time,
to a point where one cannot rectify it for it is too late.  It is here where Okeke is
located in that he cannot shake the feeling that time and mortality will rob him of his
opportunity to bring a sense of peace to the situation.  In this, external becomes
internal quite quickly.