"The story of King David is about switching from a nomadic life to one of agriculture"
The story of King David was one of his being part of a shepherd family, then anointed King because Saul had lost God's favor, but not yet able to take kingship becauese he was being hunted by Saul who wanted to kill him. David killed Goliath which raised his stature with the people, thus raising Saul's jealousy! That was the reason for David's earlier wanderings.
So his people were nomadic and eventually wound up settled in one place?
I've read that's what the story of Cain & Abel was about.