David slaughtering Amalekites. From Bible Encyclopedia.
In this chapter, David is still worried about King Saul, and is essentially scared that Saul is going to kill him. That's right. He's still paranoid about Saul even after sparing Saul's life and Saul admitting that David is favored by their god Yahweh.
So, David fled with his 600 men, went into Philistine and - as usual - embarked on a campaign of slaughtering other tribes. Among these tribes that were slaughtered were the Amalekites, whom if you remember were already slaughtered by Saul just a few chapters back.
And that got me to thinking - why all this animosity toward the Amalekites?!? Who were they? Well, after some research it seems they were from the same ethnic group as the Hebrews, but their tribe was probably much more ancient. However, the animosity apparently comes from the legends surrounding the Israelites return from slavery under the Egyptians. While on their Exodus, the Amalekites attacked them, and ever since then the Amalekites have been vilified by the Israelites.
I guess this animosity towards the Amalekites keeps manifesting in Israelite writing in the form of them being utterly annihilated - again and again and again. I suspect there will be more Amalekite slaughtering in the chapters and books ahead, even though it says quite clearly here "And David smote the land, and left neither man nor woman alive ..."
If you remember from previous chapters, the same thing is always said about the Israelite's massacres and genocides.