Sforno on Genesis 13:7/ספורנו על בראשית י״ג:ז׳

1ויהי ריב בין רועי מקנה אברם ובין רועי מקנה לוט, there was an argument between who would succeed to drive out the other from the available grazing land they would find.

2והכנעני והפריזי אז יושב בארץ. This is why a quarrel between two brothers who lived side by side was especially embarrassing and harmful to the image of Avram among the surrounding tribes. When those tribes would see the brothers quarrel, they would assume that neither of them was a peace-loving individual and they would reason that they had even more reason to quarrel with either one of those recent immigrants.