Who are "ha'Amonim"?
'Rashi' and Radak, from Yalkut Shimoni 764: They are Amalek. They are called Amonim because they changed their dress and language to be like Amonim, lest Yisrael recognize them, and mixed with them and came to fight against Yisrael 1 . So it is proven below (22:22-23). So ha'Kalir wrote in a Piyut - Zechor Aritz b'Amonim Nechba Feretz Karmei Ein Gedi - remember what the tyrannical Amalek did. He hid among Amonim, and came to breach the vineyards of Yisrael - "v'Hinam b'Chatzetzon Tamar Hi Ein Gedi", and Ein Gedi is near Amalek - "va'Yaku Es Kol Sede ha'Amaleki v'Gam... b'Chatzetzon Tamar."
Radak: They are another nation called Amonim based on their place. Bnei Amon are always called so; they are never called Amonim. Also below it says "va'Yitenu ha'Amonim Minchah l'Uziyah"; perhaps they are the Me'unim mentioned there (26:7-8); the letters Ayin and Mem are reversed. This is correct; their place was Ma'on. We find "v'Tzidonim v'Amalek u'Ma'on."
Malbim: Below (22:22-23) it says that they dwelled in Har Se'ir. We must say that Amonim dwelled there at the time.
Radak: They were subservient to Malchei Yehudah, until they rebelled in the days of Yehoram ben Yehoshafat.
