Genesis 13 is remarkable for what it tells us about Abram. Far from being a solitary individual, he was the chieftan of a rather extensive entourage (later we learn he had over 300 trained soldiers in is camp) with people, livestock, tents and personalty in abundance. When Abram came to town, you knew it. He needed a lot of space for his people and animals. Lot, his nephew, was also endowed with a large following, and it was decided that Abram and Lot needed to split up so as not to exceed the carrying capacity of the land. Lot went to the Jordan Valley and settled in Sodom. When Lot leaves, God reiterates His promise to Abram that his would be all the lands that he could see. Again, we don't have any way of knowing whether God actually made this promise to Abram or how he communicated it. It doesn't really matter.
In chapter 14, Abram and his trained men went to the rescue of Lot who had been taken prisoner in a war among various kingdoms. Abram defeated Chedorlaomer and brought back the people and their goods. The King of Sodom meets him and tells him to keep the goods but leave the people, but Abram declines to take anything except what his men and his allies have eaten. Melchizedek, priest of the God Most High makes an appearance.
In chapter 15, Abram begins to doubt the promise of God since he has no heirs of his body. But God tells him to put some sacrificial animals on an altar which, as a sign, manifest a smoking oven and a flaming torch between the pieces of dead animal. God qualifies His promise by pointing out that Abram's seed will be enslaved in a strange land for four centuries but would afterwards return to Canaan. This makes me think that God may not have been all that clear in His promise, that perhaps the message wasn't delivered personally. I mean, who would gainsay God Almighty if He is telling you something to your face? Who would need such a sign (which is far more equivocal than the promise)? If the promise was made, I reckon it was made through priests or in dreams or some such way. More likely, this was just made up after the fact to conform to what the authors thought had happened. As a literary device, it works. As a statement of historical fact, not so much.