יְהוָ֤ה אֱלֹֽהֵיכֶם֙ הַהֹלֵ֣ךְ לִפְנֵיכֶ֔ם ה֖וּא יִלָּחֵ֣ם לָכֶ֑ם כְּ֠כֹל אֲשֶׁ֨ר עָשָׂ֧ה אִתְּכֶ֛ם בְּמִצְרַ֖יִם לְעֵינֵיכֶֽם׃
Der HERR, dein Gott, der vor dir geht, wird für dich kämpfen nach allem, was er in Ägypten vor deinen Augen für dich getan hat;
Rashi on Deuteronomy
ילחם לכם means, [HE WILL FIGHT] ON YOUR BEHALF.
Haamek Davar on Deuteronomy
He will wage war for you. Hashem’s intent was not that the Canaanites should be smitten by plague before they arrived to wage war, but that He would help the Jews while they were fighting against them.
Haamek Davar on Deuteronomy
As in everything that He did with you. With the Egyptians — Hashem did not destroy them beforehand but waged war against them at the Red Sea. This was His Will and His Honor, and similarly in the war against the Canaanites.