Chukat #2: Who caused the children of Ammon to inherit?

Two perspectives.
In parshat Devarim {Devarim 2:18-19}, God tells Moshe:

יח אַתָּה עֹבֵר הַיּוֹם אֶת-גְּבוּל מוֹאָב, אֶת-עָר.	18 'Thou art this day to pass over the border of Moab, even Ar;
יט וְקָרַבְתָּ, מוּל בְּנֵי עַמּוֹן--אַל-תְּצֻרֵם, וְאַל-תִּתְגָּר בָּם: כִּי לֹא-אֶתֵּן מֵאֶרֶץ בְּנֵי-עַמּוֹן לְךָ, יְרֻשָּׁה--כִּי לִבְנֵי-לוֹט, נְתַתִּיהָ יְרֻשָּׁה.	19 and when thou comest nigh over against the children of Ammon, harass them not, nor contend with them; for I will not give thee of the land of the children of Ammon for a possession; because I have given it unto the children of Lot for a possession.--

That is, Hashem has given it to them as an inheritance/possession.

Meanwhile, in sefer Shofetim, in Shofetim 11:23-24, Yiftach tells the king of the children of Ammon:

כג וְעַתָּה ה אֱלֹקֵי יִשְׂרָאֵל, הוֹרִישׁ אֶת-הָאֱמֹרִי, מִפְּנֵי, עַמּוֹ יִשְׂרָאֵל; וְאַתָּה, תִּירָשֶׁנּוּ.	23 So now the LORD, the God of Israel, hath dispossessed the Amorites from before His people Israel, and shouldest thou possess them?
כד הֲלֹא אֵת אֲשֶׁר יוֹרִישְׁךָ, כְּמוֹשׁ אֱלֹהֶיךָ--אוֹתוֹ תִירָשׁ; וְאֵת כָּל-אֲשֶׁר הוֹרִישׁ ה אֱלֹקֵינוּ, מִפָּנֵינוּ--אוֹתוֹ נִירָשׁ.	24 Wilt not thou possess that which Chemosh thy god giveth thee to possess? So whomsoever the LORD our God hath dispossessed from before us, them will we possess.

So, while Hashem gives the Israelites their inheritance, Chemosh gives the children of Ammon their inheritance.

One need not say that Yiftach believed this. This was diplomacy, and da lifnei ata omed, Yiftach knew that his intended audience was an idolator who followed Chemosh, and so he spoke to him in a way that he hoped would be successful.