So did God intentionally hand the world over to "his adversary" or was God unable to stop "his adversary" from taking it?
When Jesus was baptized, he retreated into the wilderness alone because the account says that "the heavens were opened up" and because Jesus was 100% human, it was only then that he was endowed with holy spirit and all memory of his past existence in heaven came flooding back. For 40 days he remained, communing with his Father, preparing for the difficult mission he was about to undertake.
When he returned, the devil took no time to begin his temptations, targeting his hunger (he had not had any food all that time, obviously physically sustained by God in some way) appealing to his ego, and testing his trust in his God. (Luke 4:1-13)
In Luke 4:5-8 we see one of the temptations was to offer Jesus all the kingdoms of the world in exchange for just one act of worship. He said that all authority over these kingdoms were his because they had been "delivered" to him....and he also said that 'he could give rulership to whomever he wished'. He could not offer the son of God something that was not his to give....and Jesus did not challenge his claims.
Why would God "deliver" rulership of the world over to his adversary? Because this 'pretender' had made accusations about God's sovereign right to set limits for his creation, and basically called him a liar and suggested that humans would be better off making their own decisions....that they don't need God at all. Sound familiar? Has anything changed?
So the best way for God to settle this issue once and for all, was to hand rulership of the human race over to the one they chose to obey. Satan then became the god and ruler of this world. (1 John 5:19; 2 Corinthians 4:3-4)
Since
telling the humans that they needed to abide by his commands (given only for their good) didn't prompt their obedience, then
showing them what happens when he withdraws his protection and blessings from them would clearly demonstrate that they cannot exercise self determination, (whilst ignoring God's direction) without serious consequences. We are living in the outcome of that demonstration.....the world is in an awful mess, politically and socially, as well as affecting so many, mentally, emotionally and physically.....regardless of our progress in science and technology, humans cannot successfully rule themselves.
We have reached the real possibility of committing self-annihilation. I believe God will step in before we reach that situation. (Isaiah 55:11)
And where did this "adversary" come from?
According to scripture, the adversary was a beautiful angel stationed in Eden as a guardian. (Ezekiel 28:13-15) But he abused his position of trust and his free will, and plotted a way to make himself a god. He wanted worship as he demonstrated with Jesus, and humans are the only ones who can give it to him. He had already tricked two perfect humans into doing his bidding and the perfect Jesus would have been another feather in his cap. Jesus showed by his steadfast obedience that Adam and his wife had no excuse to cave.
Satan also demonstrated with Job, how malicious his intent is concerning humans. He doesn't care about their welfare, only what he can gain from exploiting their disobedience. He will make humans pay for staying faithful (the reason why the road to life is "cramped and narrow" is not because God makes it so. Matthew 7:13-14) Staying faithful in this world is hard because satan makes it so.
The only way to get what he wanted was to separate the humans from their God by tricking them into disobedience. He wasn't successful with Job and he wasn't successful with Jesus or any of the other faithful servants down through time. Will he be successful with us? Only we can answer that.
He hasn't ever changed his tactics. But how do you fight an enemy that you don't believe exists?