Why does it say "ha'Vanim Ein l'Yisrael"?
Rashi: This is said in astonishment. Therefore there is no Dagesh in the Beis, and there is Chataf Patach under the Hei. Malbim - if Yisrael [who were exiled from Ever ha'Yarden] do not have children, do they not have other heirs?! (Why did Malkam take Eretz Gad?)
What is "Malkam"?
Rashi: It is the idolatry of Amon 1 - "ul'Milkom To'avas Bnei Amon" (Melachim II, 23:13).
Radak: Perhaps Amon's king built his capitol in Eretz Gad.
Refer to Bamidbar 21:29:2:2 and the note there.
When did Amon take Gad?
Radak: When Bnei Gad and Bnei Reuven were exiled from their land, Bnei Amon and Mo'av came and dwelled there; they were neighbors. They also thought that they were entitled to it, for it was theirs earlier (but Sichon and Og took it from them). "Gad" refers to Eretz Gad.
Malbim: [What used to be] Amon's land was given to Gad (Yehoshua 13:25).
