Another aspect of דרכי שלום has to do with our interaction with non-Jews. The Mishna in גיטין mentions the importance of allowing Gentile poor to come into our fields in order to partake of the same crops left over for Jewish poor. This is to keep peaceful relations with them.
The Gemara expands on this idea and says that it is also our duty to visit the sick of the non-Jews as well as burying their dead. The Torah obligation is to leave over parts of our field (לקט פיאה שכחה), as well as visiting the sick, and caring for the dead, applies specifically to Jews. However, the Rabbis instituted under the heading of דרכי שלום, to apply this to non-Jews.
A friend of mine worked as a street sweeper in Jerusalem and once found 140,000 shekels cash that belonged to an Arab. He returned the money and did not even get a thank you. I told him that he did a big Kiddush Hashem. He was rewarded in other ways for fulfilling the rabbinical decree of דרכי שלום.