I would say that the theme revealed by this conflict in the excerpt is <em>grief / sorrow.</em>
Explanation:
In this excerpt, the speaker talks from a very sensitive position, talks about how beautiful their lives was, like if he or she felt nostalgic about the life they had, and how difficult it is to let go. It feels that the speaker is talking about the grief process, the sorrow he / she feels "<em>for each poor ghost unfleshed by the Cicones on that field</em>".
The entire premise of the story is that two men are hunting each other on account of hatred derived from a centuries old land dispute. Society Notwithstanding the ingrained hatred the two men have for each other, they recognize the societal constraints placed on would-be-murderers.
