Why did Abram and Lot experience strife?
Abram and Lot experienced strife because their combined wealth and substance had become so great that the land could not support them dwelling together. The available territory was not able to bear both households and their possessions, creating conflict and argument between them.
Les explains that Lot also went with Abram, but the land was not able to bear them, and they could not dwell together because between the two of them their substance was so great. As might be expected, strife and a lot of argument followed. Human nature hasn't changed one iota. Finally Abram, the more godly of the two, told Lot they should not argue or have strife, and asked whether the whole land was not before him.
And the land was not able to bear them, that they might dwell together: for their substance was great, so that they could not dwell together.