Why will the thousand-year period known as the "Millennium" be such a time of peace and bliss?

Let's allow the Bible to give you the answer:
Then I saw an angel coming down from heaven, having the key to the bottomless pit and a great chain in his hand. He laid hold of the dragon, that serpent of old, who is the devil and Satan, and bound him for a thousand years;

and he cast him into the bottomless pit, and shut him up, and set a seal on him, so that he should deceive the nations no more till the thousand years were finished. But after these things he must be released for a little while.

And I saw thrones, and they sat on them, and judgment was committed to them. Then I saw the souls of those who had been beheaded for their witness to Jesus and for the word of God, who had not worshiped the beast or his image, and had not received his mark on their foreheads or on their hands.

And they lived and reigned with Christ for a thousand years.... Blessed and holy is he who has part in the first resurrection. Over such the second death has no power, but they shall be priests of God and of Christ, and shall reign with Him a thousand years.
(Rev. 20:1-4,6)
After Jesus returns to the earth, the devil will be locked up for a thousand years. Jesus will remain on the earth and rule over the nations; He will permit us to help Him.

The thousand-year period will be a time of peace and bliss because there will be no devil and Jesus will reign as King!

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