The term, "The God Of This World", a.k.a. "The God Of This Age", is a euphemism for Satan. The term originates in 2 Corinthians 4:4.
In whom the god of this world hath blinded the minds of them which believe not, lest the light of the glorious gospel of Christ, who is the image of God, should shine unto them.
The term has very gnostic overtones and refers to the belief that after Adam & Eve ate from the fruit of the tree of the knowledge of good and evil, that control of the earth and humanity was temporarily given unto Satan, so that Satan should rule over mankind until the time of the Second Coming and Judgement Day.
Many Christians seem to not understand that Satan controls the world. Many a Christian today who may be fully aware of the above verse and meaning of the phrase, will still vote for say a "Christian" candidate for presidency or other office. If such Christians truly understood that Satan is boss then they would realize it doesn't matter if they vote for a man, or woman, who claims to be Christian. Satan is going to get his chosen man, or woman, in office.