God created the world to be good. However, humans sinned and chose to listen to Satan instead of listen to God.
When humans chose to listen to Satan, they gave dominion of the world to him.
Humans listened to Satan who told them that it was ok to eat from a forbidden tree.
"The serpent said to the woman, 'You surely will not die! For God knows that in the day you eat from it your eyes will be opened, and you will be like God, knowing good and evil.'" (Genesis 3:4-5)
But God had said: "From any tree of the garden you may eat freely; but from the tree of the knowledge of good and evil you shall not eat, for in the day that you eat from it you will surely die." (Genesis 2:16-17)
The tree of the knowledge of good and evil was a test for Adam and Eve. God and the good angels were already at war with evil caused by Satan and his fallen angels. So God knew good and evil in the sense of being good and warring against evil. God would have shielded the newly created humans from Satan and his fallen angels completely if Adam and Eve passed the test.
If they passed the test and did not eat from the tree, they would only know good.
But they failed the test, so they committed evil and experienced evil.
When the first couple listened to Satan instead of to God, the dominion of the world was given to Satan.
That was why Satan later on said to Jesus that he would give Jesus all the kingdoms of the world if Jesus worshipped Satan:
"Again, the devil took Him to a very high mountain and showed Him all the kingdoms of the world and their glory; and he said to Him, 'All these things I will give You, if You fall down and worship me.'" (Matthew 4:8-9)
Jesus did not dispute with Satan that the world was his or not. Instead Jesus said: "Go, Satan! For it is written, ‘You shall worship the Lord your God, and serve Him only.’ ” (Matthew 4:10)
In fact, the Bible says that God wants to take people from the world as His own possession:
"For the grace of God has appeared, bringing salvation to all men, instructing us to deny ungodliness and worldly desires and to live sensibly, righteously and godly in the present age, looking for the blessed hope and the appearing of the glory of our great God and Savior, Christ Jesus, who gave Himself for us to redeem us from every lawless deed, and to purify for Himself a people for His own possession, zealous for good deeds." (Titus 2:11-14)
So God doesn't have dominion over the world currently. Otherwise, He would not need to purify a people for His own possession if they already belong to Him.
But this world is sinful and belongs to Satan.
A person can choose to listen to Satan and continue to practice sinful deeds. If a person chooses to listen to Satan, then he belongs to Satan and Satan rules in his heart.
However, we can personally choose to belong to God.
If a person chooses to listen to God by believing in Jesus and obeying Him, then he belongs to God and God rules in his heart.
What do you choose?