Amos 1:13

He now prophesies against the Ammonites, who also derived their origin from the same common stock; for they were the posterity of Lot, as it is well known; and Lot was counted as the son of Abraham, as Abraham, having taken him with him from his country brought him up, no doubt, as his own son. Then Abraham was the common father of the Jews and of the Ammonites. Now, when the children of Ammon, without any regard to relationship, joined their forces to those of enemies, and conspired together, their cruelty admitted of no excuse. And there is no doubt but that they were guilty of many other crimes; but God, by his Prophet, enumerates not all the sins for which he had purposed to punish them, and only points out distinctly, as in passing, but one sin, and generally declares, that such people were utterly past hope, for they had hardened themselves in their wickedness.

He therefore says of the children of Ammon, that they rent the pregnant women Some take הרות, erut, for הרים, erim, mountains; but I see not what can induce them, unless they think it strange that pregnant women were rent, that the Ammonites might extend further their borders; and for this ends it would be more suitable to regard the word as meaning mountains; as though he said, “They have cut through mountains, even the earth itself; there has been no obstacle through which the Ammonites have not made their way: an insatiable cupidity has so inflamed them, that they have rent the very mountains, and destroyed the whole order of nature.” Others take mountains metaphorically for fortified cities; for when one seeks to take possession of a kingdoms cities stand in his way like mountains. But this exposition is too strained.

Now, since הרות, erut, mean women with child, the word, I doubt not, is to be taken in its genuine and usual sense, as we see it to be done in Hosea. [Hosea 13:16.] But why does the Prophet say, that the Ammonites had rent pregnant women? It is to show, that their cupidity was so frantic, that they abstained not from any kind of cruelty. It is possible that one be so avaricious as to seek to devour up the whole earth, and yet be inclined to clemency. Alexander, the Macedonian, though a bloody man, did yet show some measure of kindness: but there have been others much more cruel; as the Persian, of whom Isaiah speaks, who desired not money, but shed blood, (Isaiah 13:17) So the Prophet says here of the Ammonites, that they not only, by unlawful means, extended their borders, used violence and became robbers who spoiled others of their property, but also that they did not spare even women with child. Now this is the worst thing in the storming of towns. When a town has wearied out an enemy, both pregnant women, and children, and infants may, through fury, be destroyed: but this is a rare thing, and never allowed, except under peculiar circumstances. He then reproaches the Ammonites, not only for their cupidity, but also for having committed every kind of cruelty to satisfy their greediness: they have then torn asunder women with child, that they might extend their borders.