Notice what the Bible says:
"Satan, the god of this evil world." (2 Cor. 4:4) NLT
"The whole world is under the control of the evil one." (1 John 5:19) NIV
"And the great dragon was thrown down, the serpent of old who is called the devil and Satan, who deceives the whole world." (Rev. 12:9) NASB
When Jesus was "tempted by the Devil," Jesus didn't question Satan's role as the ruler of this world. The Bible explains what happened: "The Devil took him along to an unusually 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 do an act of worship to me.' Then Jesus said to him: 'Go away, Satan!'" - Matthew 4:1, 8-10
But the Bible assures that this situation will not last forever:
"The world [including Satan as ruler] is passing away, but he that does the will of God remains forever." (1 John 2:17) The beneficial results of this are described in the following verses: Psalm 37:9-11, 29; 2 Peter 3:13; Revelation 21:3, 4.
For more, see:
Satan
If God is good why did he make bad things like wars, sickenss and pain? (jwitness forum; Links to videos included)
Who Really Rules the World? (WBTS)
Who Is the Devil? (WBTS)
Does God Really Care About Us? (WBTS)
Search For Bible Truths - ARCHIVE
Scriptures Index
Search For Bible Truths - Search Guide