They returned home in great anger - They thought they were insulted, and began to meditate revenge. See the notes on 2 Kings 14:1-20 (note), where almost every circumstance in this chapter is examined and explained.

And other ten thousand No intimation is given on what account, or on what provocation, this most cruel conduct towards the prisoners of war was adopted. The enmity between israel and Edom seems to have been reciprocal and deeply malignant. The victorious king and his army considered every individual of Edom as a traitor and rebel; and so adjudged them to death, and acted on this judgment. But their conduct was wholly inexcusable, and could only perpetuate rancour to future generations, and provoke the surviving Edomites to cruel retaliations, whenever they had it in their power.

cast them

2 Samuel 12:31 And he brought forth the people that were therein, and put them under saws, and under harrows of iron, and under axes of iron...

1 Chronicles 20:3 And he brought out the people that were in it, and cut them with saws, and with harrows of iron, and with axes...

broken in pieces

2 Chronicles 20:10 And now, behold, the children of Ammon and Moab and mount Seir, whom you would not let Israel invade...

2 Chronicles 21:8-10 In his days the Edomites revolted from under the dominion of Judah, and made themselves a king...

The Unmerciful Servant.
"Therefore is the kingdom of heaven likened unto a certain king, which would take account of his servants. And when he had begun to reckon, one was brought unto him, which owed him ten thousand talents. But forasmuch as he had not to pay, his lord commanded him to be sold, and his wife, and children, and all that he had, and payment to be made. The servant therefore fell down, and worshipped him, saying, Lord, have patience with me, and I will pay thee all. Then the lord of that servant was moved …
William Arnot—The Parables of Our Lord