. . . and they (those in the first resurrection of the dead) lived and reigned with Christ a thousand years (Millennium) . . . they shall be priests of God and of Christ (Revelation 20:4, 6, HBFV throughout)
Before the Millennium can begin, however, Jesus Christ must return to earth a second time (Second Coming) to rule as King of Kings and Lord of Lords (Revelation 17:14, 19:16). As he returns, Satan and his human forces will wage war on the returning Savior. The ensuing battle will be unlike any war humans have ever fought.
In spite of all the planning, preparation, weapons, etc. humans will use to fight Christ, the outcome is guaranteed to be a perfect defeat (Revelation 19:11 - 21). With humans, even those who lose a war inflict a certain degree of loss, pain, suffering, trials, etc. on their enemies. While those who try to stop Jesus will suffer immeasurably (verses 17 - 21), the forces of righteousness will not suffer ANY loss whatsoever.
The millennium will be an unparalleled and unbroken period of peace and prosperity. Satan will be spiritually bound for the entire time (Revelation 20:1 -3) and therefore unable to deceive mankind. Jesus and His resurrected saints will rule the earth from Jerusalem, where mankind will flow to seek and pray to God (Zechariah 8:20 - 23).
Animals will have a peaceful demeanor in the millennium and nothing will be hurtful or destructive (Isaiah 11:6 - 9, 65:25, Ezekiel 34:25, 28, Hosea 2:18, Micah 4:1 - 4). The truth of the Bible will flow out and reach all humans no matter where they live.
They shall not hurt nor destroy in all My holy mountain; for the earth shall be full of the knowledge of the LORD, as the waters cover the sea (Isaiah 11:9).
And they will no longer teach every man his neighbor, and every man his brother, saying, "Know the Lord" because all will know Me . . . (Hebrews 8:11).
After the Millennium, God will release Satan out of his spiritual prison. The Adversary will try to fight him one last time. The devil will not only experience, yet again, a total and complete failure to take control of the universe, he will have his life extinguished FOREVER (see our article concerning what is the ultimate fate of Satan).