Psalm 59:11 Do not slay them, or my people will forget; Scatter them by Your power, and bring them down, O Lord, our shield. I remember wondering about that verse. He's not asking for Divine mercy for his foes (he explicitly asks that they be punished!), but he's asking that they be kept around--presumably as foes still, just not powerful.
History books aren't very powerful reminders. Movies can be, but over time the hunger for new stuff changes the focus. Mad studied this a while back:
And after a while you get a generation that does not know Joseph, or in our case doesn't know much about war or freedom or have much idea how hard it was to produce their inheritance.