Does the Bible prophesy a big war (like a World War 3)? Does it mention millions dying before Jesus Christ's return?
There are and will be insurmountable problems, including war, but Christ will use the trouble to demolish the old, sin-sick governments and institutions. Christ will cut short the wars to establish His righteous reign on earth. Matthew 24:21, 22 (RSV), “there will be great tribulation, such as has not been from the beginning of the world until now, no, and never will be. And if those days had not been shortened, no human being would be saved; but for the sake of the elect those days will be shortened."
The nations will be gathered for war in Armageddon. Revelation 16:14, 16 (NASB), “spirits of demons, performing signs, which go out to the kings of the whole world, to gather them together for the war of the great day of God, the Almighty…And they gathered them together to the place which in Hebrew is called Armageddon.”
At Jerusalem, God will make Himself known, and fight for Israel again! Zachariah 14:2,3 (NASB), “I will gather all the nations against Jerusalem to battle, and the city will be captured…Then the LORD will go forth and fight against those nations, as when He fights on a day of battle."
God is angry with all the oppression in the world. He will free mankind from the tyranny of evil. Zephaniah 3:8-9 (NKJV), “Therefore wait for Me,” says the LORD, “Until the day I rise up for plunder; My determination is to gather the nations to My assembly of kingdoms, to pour on them My indignation, all My fierce anger; All the earth shall be devoured with the fire (symbolic of destruction) of My jealousy. For then I will restore to the peoples a pure language, that they all may call on the name of the LORD, to serve Him with one accord.”
Christ is controlling this demolition; therefore He returns to supervise the demolition. Nothing is out of control. He does everything through wisdom, justice, love, and power. Daniel 2:44 explains, "in the days of those kings the God of heaven will set up a kingdom which shall never be destroyed…It shall break in pieces all these kingdoms and bring them to an end, and it shallstand forever."
The Bible doesn't tell us how many will die. But after the trouble, all mankind will be resurrected and rejoice! Everyone has been longing for Christ's blessed reign since the fall in Eden. Romans 8:20,21(CSB), "For the creation was subjected to futility — not willingly, but because of him who subjected it — in the hope that the creation itself will also be set free from the bondage to decay into the glorious freedom of God’s children."
The Bible tells people how to weather this trouble: "Seek the LORD, all you humble of the earth, who carry out what he commands. Seek righteousness, seek humility; perhaps you will be concealed on the day of the LORD’s anger," Zephaniah 2:3 (CSB). "Have faith in God," Mark 11:22.