In Book 6 of the Iliad, we move from the macro to the micro - on the battlefield, a single Trojan and a single Greek discovered that their grandfathers were friends, which makes them also friends.
After a long speech where Glaucus tells the story of his grandfather, Diomedes opens his arms in friendship:
He [Diomedes] spoke, and transport fill’d Tydides’ heart;
In earth the generous warrior fix’d his dart,
Then friendly, thus the Lycian prince address’d:
“Welcome, my brave hereditary guest!
Thus ever let us meet, with kind embrace,
Nor stain the sacred friendship of our race.
Know, chief, our grandsires have been guests of old;
Œneus the strong, Bellerophon the bold:
Our ancient seat his honour’d presence graced,
Where twenty days in genial rites he pass’d.
The parting heroes mutual presents left;
A golden goblet was thy grandsire’s gift;
Œneus a belt of matchless work bestowed,
That rich with Tyrian dye refulgent glow’d....
Mindful of this, in friendship let us join;
If heaven our steps to foreign lands incline,
My guest in Argos thou, and I in Lycia thine.
Enough of Trojans to this lance shall yield,
In the full harvest of yon ample field;
Enough of Greeks shall dye thy spear with gore;
But thou and Diomed be foes no more.
Now change we arms, and prove to either host
We guard the friendship of the line we boast.”
Thus having said, the gallant chiefs alight,
Their hands they join, their mutual faith they plight;
So basically, since their grandfathers were once friends, Glaucus and Diomedes swore friendship there on the battlefield. They still had to kill other Trojans and Greeks, but they would no more try to kill each other, to honor the historical friendship of their ancestors.
Another Epic Change of Heart
Likewise, in the Book of Mormon, the sons of King Mosiah go to the lands of the Lamanites, who were the enemies of the Nephites, despite the fact that they all descended from one family. But it wasn't this ancient kinship that brought these two groups together - it was the gospel of Jesus Christ.
The king's son Ammon teaches the gospel to King Lamoni, who ruled over a branch of the Lamonite nations. After his miraculous conversion and all his household, the change of heart toward Ammon and his brothers and his people was dramatic in Alma 23:
Behold, now it came to pass that the king of the Lamanites sent a proclamation among all his people, that they should not lay their hands on Ammon, or Aaron, or Omner, or Himni, nor either of their brethren who should go forth preaching the word of God, in whatsoever place they should be, in any part of their land.
Yea, he sent a decree among them, that they should not lay their hands on them to bind them, or to cast them into prison; neither should they spit upon them, nor smite them, nor cast them out of their synagogues, nor scourge them; neither should they cast stones at them, but that they should have free access to their houses, and also their temples, and their sanctuaries.
And thus they might go forth and preach the word according to their desires, for the king had been converted unto the Lord, and all his household; therefore he sent his proclamation throughout the land unto his people, that the word of God might have no obstruction,
but that it might go forth throughout all the land, that his people might be convinced concerning the wicked traditions of their fathers, and that they might be convinced that they were all brethren, and that they ought not to murder, nor to plunder, nor to steal, nor to commit adultery, nor to commit any manner of wickedness.
And now it came to pass that when the king had sent forth this proclamation, that Aaron and his brethren went forth from city to city, and from one house of worship to another, establishing churches, and consecrating priests and teachers throughout the land among the Lamanites, to preach and to teach the word of God among them; and thus they began to have great success.
And thousands were brought to the knowledge of the Lord...
And now it came to pass that the king and those who were converted were desirous that they might have a name, that thereby they might be distinguished from their brethren; therefore the king consulted with Aaron and many of their priests, concerning the name that they should take upon them, that they might be distinguished.
And it came to pass that they called their names Anti-Nephi-Lehies; and they were called by this name and were no more called Lamanites.
And they began to be a very industrious people; yea, and they were friendly with the Nephites; therefore, they did open a correspondence with them, and the curse of God did no more follow them.
Instead of sacred rules of hospitality that brought people together, in this case, it was the sacred teachings of Jesus Christ which the Lamanites learned and accepted, and their former enemies became friends, united in the brotherhood of God.
