In Act III, scene i, we learn that Duke Frederick wants revenge against Orlando. He orders Oliver to seek out Orlando and return him to the court. If Oliver fails, Frederick will dispossess him of everything he owns and be prevented from earning a living in the kingdom. The last we see of Oliver until Act IV, scene iii, is that he swears he never loved Orlando as he undertakes to obey the duke's orders to find him:
O that your highness knew my heart in this!
I never loved my brother in my life.
When next he appears, we learn how Oliver's hatred toward Orlando is transformed into love. In a flashback, he tells Celia and Rosalind, as Aliena and Ganymede, with "this bloody napkin" in his hand, how he encountered Orlando and how he was saved by Orlando from a hungry lioness in the forest. Following their reunion, which was washed in purifying tears, "from the first to last betwixt us two / Tears our recountments had most kindly bathed," Duke Senior blessed their reunion and their mutual forgiveness of each other since their life and death experience had transformed their hatred to love through courage and sacrifice leading to forgiveness. Oliver says of "the gentle duke":
[He] gave me fresh array and entertainment,
Committing me unto my brother's love;
Frankly, it's hard to know how this example might relate to today's world-wide situation because the catalyst for igniting love from Oliver toward Orlando and for reawakening early love from Orlando toward Oliver was impending death under the claws of a hungry lioness, which led to courage and self-sacrifice from Orlando. Previously, when Orlando first recognized Oliver, after the snake slithered away from his throat, Orlando had no desire to aid him.
It was a battle of moral conscience--which weighed the value of human life in the face of danger against the value of animosity and enmity--that led to Orlando's decision. A great impetus was needed for Orlando to choose on the side of humanity and turn his back upon his personal perspective. From this, the supposition can be suggested that without such life and death circumstances and such courage and self-sacrifice, ingrained hatred cannot be cast out. The simple answer, however, is that Orlando and Oliver's situation applies today by showing that the battle of moral conscience must give the victory to valuing humanity above valuing personal sentiment and embitterment.