Albert Barnes Commentary Deuteronomy 20:1

"When thou goest forth to battle against thine enemies, and seest horses, and chariots, [and] a people more than thou, thou shalt not be afraid of them; for Jehovah thy God is with thee, who brought thee up out of the land of Egypt." — Deuteronomy 20:1 (ASV)

Horses and chariots - The most formidable elements of an Eastern host, which the Canaanites possessed in great numbers; compare Joshua 17:16; Judges 4:3; 1 Samuel 13:5. Israel could not match these with corresponding forces (compare Deuteronomy 17:16, note and references), but, having the God of battles on its side, was not to be dismayed by them; the assumption being that the war had the sanction of God, and was consequently just.