if the unbelievers had fought you they would have turned their backs and then found neither protector nor helper the wont of god as in the past before and thou shalt never find any changing the wont of god.
ولو قاتلكم الذين كفروا لولوا الأدبار ثم لا يجدون وليا ولا نصيرا سنة الله التي قد خلت من قبل ولن تجد لسنة الله تبديلا