Amos 1:13

Thus says the LORD:

"For three transgressions of the Ammonites,
and for four, I will not revoke the punishment,
because they have ripped open pregnant women in Gilead,
that they might enlarge their border.

Amman has been utterly barbaric in its treatment of pregnant women. God will avenge them with fire and storm.

The terrible cruelty of Ammon was that he ripped open the pregnant women of Gilead (cf. “Gilead” in v. 3). This atrocity, sometimes a feature of ancient warfare (cf. 2 Kings 8:12; 15:16; Hosea 13:16), was designed to terrorize and decimate an enemy. The Ammonites executed this crime against defenseless women and unborn children, not for self-preservation, but simply in order to extend their borders.

As a punishment for this, their capital was to be burned, and the king, with the princes, to wander into exile, and consequently their kingdom was to be destroyed. Rabbâh, i.e., the great one, is the abbreviated name of the capital; Rabbah of the children of Ammon, which has been preserved in the ruins of Aurân (see at Deut. 3:11). The threat is sharpened by the clause בִּתְרוּעָה וגו׳, at the war-cry on the field of battle, i.e., an actual fact, when the enemy shall take the city by storm. בְּסַעַר וגו׳ is a figurative expression applied to the storming of a city carried by assault, like בְּסוּפָה in Num. 21:14. The reading מַלְכָּם, “their (the Ammonites’) king,” is confirmed by the LXX and the Chaldee, and required by וְשָׂרָיו (cf. Amos 2:3), whereas Μαλχόμ, Melchom, which is found in Aq., Symm., Jerome, and the Syriac, rests upon a false interpretation.

The Ammonites under Nahash attacked Jabesh-gilead and refused to accept the offer of the latter to save them, unless the Jabesh-gileadites would put out all their right eyes (1Sa 11:1, &c.). Saul rescued Jabesh-gilead. The Ammonites joined the Chaldeans in their invasion of Judea for the sake of plunder.
ripped up … women with-child—as Hazael of Syria also did (2Ki 8:12; compare Ho 13:16). Ammon’s object in this cruel act was to leave Israel without “heir,” so as to seize on Israel’s inheritance (Je 49:1).

Ammon was connected with Israel as being sprung from Lot, and together with Moab, which had the same origin, retained the stamp of its incestuous birth in habits, character, and worship (Gen. 19:30, etc.). Their hostility to Israel was first shown in their participation with Moab in the affair of Balaam (Deut. 23:4). Other instances are seen in their treatment of Jabesh-Gilead (1 Sam. 11:1–3) and of David’s messengers, and in hiring the Syrians to make war on David (2 Sam. 10:1–6).