Annihilation of 7 nations

The brutality of annihilation of 7 nations is subdued in Deteuronomy 9, as God says "Do not say in your heart when the LORD your God has driven them out before you, ‘Because of my righteousness the LORD has brought me in to possess this land,’ but it is because of the wickedness of these nations that the LORD is dispossessing them before you. “It is not for your righteousness or for the uprightness of your heart that you are going to possess their land, but it is because of the wickedness of these nations that the LORD your God is driving them out before you, in order to confirm the oath which the LORD swore to your fathers, to Abraham, Isaac and Jacob.
Well now the question remains of judging the brutality of these 7 types of people!!! With what parameters they were judged? Who is to decide those parameters?
They were not even given the choice to think upon the ideology of sons of Israel. They were just annihilated not even given a chance to convert. Its brutal than colonization!!