Rashi on Deuteronomy 20:13/רש"י על דברים כ׳:י״ג

1ונתנה ה' אלהיך בידך means THEN THE LORD THY GOD WILL GIVE IT INTO THY HANDS — if you have done all that is prescribed in this section the Lord will in the end give it into your hands (Sifrei Devarim 200:6).