What is the EXTERNAL CONFLICT in O. Henry's After Twenty Years?

The external conflict has to do with the twenty years
 that have passed since the two men have seen one another.  People change a lot in
twenty years, and both men have no idea what to look for in a physical appearance . 
Jimmy, the policeman, says that when Bob lit the cigar he was smoking, he recognized the
man who was wanted in Chicago, not his friend, Bob.  The only reason he knew it was his
friend was from their conversation.  Bob also did not recognize his friend.  He
befriends this man who walks up to him, but he even comments that he doesn’t remember
Jimmy having that height.  Still, he is willing to be persuaded that Jimmy grew a few
inches after he turned twenty! It wasn’t until he saw his nose --- not his full face,
but his nose, that he realizes that it isn’t his friend. Jimmy.  The problem is resolved
with the note.