The whole premise of your question that God is having a war with evil is wrong.
The premise that Satan, if he exists, is bright and cunning, but yet is dumb enough to challenge or go against God's interest is also false and illogical.
No one can challenge God. Anyone who thinks they can is definitely not bright.
Everything, even evil needs God's approval and power to exist. God is the only power that sustains everything there is
In order for God to experience his Supreme Godhead, he allowed evil to exist for this holy purpose.
Without experiencing evil one cannot know or fully experience Goodness of God. This is true for man and God.
Therefore the existence of evil is no accident. God is perfect and makes no accidents.
In order experience his Goodness, he came up with a perfect plan which include the creation imperfect beings. And so he created both the physical and spiritual universe.
God knew in advance before the creation of imperfect man that our early parent would chose path of knowledge or some see this as eating a fruit from the tree of knowledge.
This was choice was given to man out of God's own free will and should not be considered as a sin as most religions originating in the Middle-East claim. Actually this choice fits well with God's perfect plan.
You have a good question that challenges the Judea-Christian-Muslim theology. They believe that God is having a battle with evil. Actually God has no battles. If God does not like something it will cease to exist now, in the past, and and forever.