Verse 17: Then the children of Ammon were gathered together (Heb. cried together), and encamped in Gilead. And the children of Israel assembled themselves together, and encamped in (Judg. 11:11, 29; Gen. 31:49) Mizpeh.
[Shouting together] That is, calling together their men for war (Lapide).
[In Gilead] Understand, either, 1. in the half tribe of Manasseh (Lapide, Bonfrerius), which in the strict acceptation of Gilead is called (Bonfrerius): or, 2. in the tribe of the Gadites: which I would prefer, because the Ammonites were pretending that that entire tract from Aroer to Jabbok was taken from them, Judges 11:13, which was occupied by the Reubenites and the Gadites; but not that tract of land which was on the other side of the torrent Jabbok, and was possessed by the Manassites (Bonfrerius).
[In Mizpeh] It signifies a looking-glass, and so there are multiple places called Mizpeh: 1. in Judah, Joshua 15:38; 2. in Benjamin, Joshua 18:26; Judges 20:1; 3. in Moab, 1 Samuel 22:3; 4. in Naphtali, Joshua 11:3; 5. and this one (Serarius). There was a twofold Mizpeh on the other side of Jordan, as we said on Joshua 11:3, one in Gad, the other in Manasseh. This one appears to have been the latter (Bonfrerius, Lapide); both because Jephthah dwelt there, who was a Manassite, see Judges 11:1 (Bonfrerius); and because the Ammonites had invaded the tribe of Manasseh neighboring to them (Lapide).
That Mizpeh which was beyond Jordan in Gad or Manasseh; of which see Genesis 31:49; Joshua 18:26; Judges 10:17; 11:11, 29, 34. There were other cities of that name in Scripture.
Verse 18: And the people and princes of Gilead said one to another, What man is he that will begin to fight against the children of Ammon? he shall (Judg. 11:8, 11) be head over all the inhabitants of Gilead.
[He shall be the leader of the people of Gilead] Not only the general of the war, but the prince of the people of Gilead (Bonfrerius). With this reward they entice, etc., as Caleb did formerly (Martyr). And thus at that time they did indeed determine by emergency counsel, but counsel not quite correct; whence afterwards they more correctly sent for Jephthah (Lapide out of Tostatus, similarly Serarius). This they determined, perhaps in council they were not agreeing concerning choosing a Commander-in-Chief, neither was anyone daring to undertake it. But what if whoever had undertaken arms first was a wicked man? Responses: 1. They hold all civil promises in this way, if they are able to be discharged by honest men. 2. Therefore, I think that this was a sign bestowed by God, and so they were certain that an evil Prince was not be given to them. Perhaps they had asked of the Lord a Leader, and had received a response, that they were to understand by this sign who was to be received as Leader; namely, he that had first begun to fight against the enemy. Sometimes God made use of such signs without a voice or external oracle, as in Genesis 24 (Martyr).
 Hebrew: וַיִּצָּֽעֲקוּ֙ בְּנֵ֣י עַמּ֔וֹן וַֽיַּחֲנ֖וּ בַּגִּלְעָ֑ד וַיֵּאָֽסְפוּ֙ בְּנֵ֣י יִשְׂרָאֵ֔ל וַֽיַּחֲנ֖וּ בַּמִּצְפָּֽה׃
 Hebrew: וַיִּצָּעֲקוּ.
 See Joshua 12:2.
 מִצְפָּה/Mizpeh is related to the verbal root צָפָה, to look out.
 Hebrew: וַיֹּאמְר֙וּ הָעָ֜ם שָׂרֵ֤י גִלְעָד֙ אִ֣ישׁ אֶל־רֵעֵ֔הוּ מִ֣י הָאִ֔ישׁ אֲשֶׁ֣ר יָחֵ֔ל לְהִלָּחֵ֖ם בִּבְנֵ֣י עַמּ֑וֹן יִֽהְיֶ֣ה לְרֹ֔אשׁ לְכֹ֖ל יֹשְׁבֵ֥י גִלְעָֽד׃
 Joshua 15:16; Judges 1:12.