In the great tribulation the Antichrist allows no one to buy or sell, not even salt, without his name or mark (666) on the right hand or forehead, and everyone must bow to him or his image. Those who take the mark face God's wrath in the Day of the Lord, then the lake of fire, the second death: no part in the first resurrection and no place in God's eternal kingdom. Those who refuse go hungry and thirsty, and are hunted down and killed.
After the two witnesses are killed, the 144,000 carry the three angels' message across the world: fear God, Babylon is fallen, do not take the mark. It is called the "everlasting" gospel because it is preached through the whole of that time.
The covenant, and the war before it
The final seven years begin with the covenant (karaar) of Daniel 9:27:
And he shall confirm the covenant with many for one week: and in the midst of the week he shall cause the sacrifice and the oblation to cease…
— Daniel 9:27
"Many" means most of the world's nations, not all. The nations that sign give authority to the beast of Rome, the empire that became the Roman church, whose head will be a man in the office of Pope, accepted as a good, devout, God-fearing man. Satan will enter him as he entered Judas, for power changes a man's thinking. Having signed, the nations are bound for seven years.
A war comes first, the one in Ezekiel 38:1–6, where Gog of Magog gathers Rosh, Meshech, Tubal, Persia, Cush, Put, Gomer and Togarmah against Israel. These are identified as Russia (Rosh, Meshech, Magog), Iran (Persia), the African Union (Cush and Put) and eastern Europe (Gomer and Togarmah, around Ukraine and Kazakhstan). With God's intervention Israel wins; America is on its side (we do not know in what way) and, behind America, Canada, England, France and the rest of Europe. The defeated powers must accept the terms of war, and the covenant follows, creating a new body like the United Nations.
Who signs? Probably North and South America (the south being largely Catholic), Africa, Europe and Russia. China and India, with some smaller neighbours, will probably stay out; India's own principle is to side with neither America nor Russia. Australia is uncertain. Israelites fleeing the covenant lands may be told to go to China, India or other parts of Asia, though we cannot be sure.
The sixth trumpet, the second woe
The last three trumpets are three woes (Revelation 8:13). The fifth was the first; the sixth is the second:
The second woe is past; and, behold, the third woe cometh quickly.
— Revelation 11:14
At the sixth trumpet (Revelation 9:13–21) four angels bound at the Euphrates are loosed to slay a third of mankind, and the army of horsemen numbers 200 million. If the world has about nine billion people by then, against seven or eight billion today, a third is some three billion.
This is war language. John described what he saw in the words he had, so the "horses" are in fact war vehicles of various kinds, firing flame from front and back. The locusts of the fifth trumpet were spirits from the bottomless pit; this is a real army.
Where? The survivors did not turn from their idols of gold, silver, brass, stone and wood (9:20), and idol temples are found mostly in Asia: above all India, and also China, Japan, Malaysia, the Philippines and Indonesia. Only India can match China in Asia, so a war between those two is very likely, though we cannot be certain. Each has about one and a half billion people, which together make the three billion. The covenant nations will not intervene, since neither is in their covenant: sort it out yourselves.
Meanwhile, inside the covenant countries, God's people are being hunted and killed. Both go on until near the end of the 1,260 days, and the war then widens, with armies moving towards Israel, the subject of the next session.
The martyrs
Revelation 7:9–17 shows a great multitude from every nation, in white robes:
These are they which came out of great tribulation, and have washed their robes, and made them white in the blood of the Lamb.
— Revelation 7:14
They are Gentiles who repented, believed, were baptised in the name of the Lord Jesus Christ and received the Spirit, but were not taken up with the bride. Because they refused the name and mark they could not buy or sell; they went hungry and thirsty, fled and hid, suffered the sun's heat and wept, and many were caught and killed. Their spirits went up to the Lord, and Revelation 7:16 promises them no more hunger, thirst or scorching sun, the very things they suffered.
Revelation 15:2–4 shows a second company on the sea of glass, victors over the beast, his image and the number of his name, singing the song of Moses and the song of the Lamb. They are Jews, the remnant of the woman's seed, killed by the Antichrist. They sing Moses' song as Jews and the Lamb's as believers in Christ, and they say that all nations, not only their own, will come and worship before the Lord.
The harvest of the earth
Revelation 14:14–16 shows one like the Son of Man on a white cloud, with a golden crown and a sharp sickle, while an angel cries that the harvest of the earth is ripe. The crop is people. As in Jesus' parable of the wheat and the tares, this is the reaping of the wheat, the good people, since it is Jesus who reaps.
At the end of the 1,260 days, before the day of wrath, the Lord gathers all His people: the believing Gentiles who refused the mark, and the Jews who believed in Christ, killed by the Antichrist. The harvest goes on until their full number is in, some by martyrdom, perhaps others by natural death. Then the Day of the Lord follows, with Daniel's 75 extra days (1,290 and 1,335), to be taken up next time.
Takeaway
Refuse the Antichrist's name and number, whatever it costs. Those who do are washed in the Lamb's blood and stand before God's throne, and the Lord gathers all His people before His wrath is poured out.