The Day [time frame] of the Lord will begin with His coming judgment of the tribulation period which He will bring against an unbelieving world. This 2,550 day time frame will begin without warning to the inhabitants of the earth and it will include all of the related events recorded in the prophetic visions of the Bible prophets for the period. None of these things will be covert and observable on the earth until the time frame begins. There has been and is a great deal of speculation regarding the details, signs, and events of the time frame related to present observable earthly events, but the things contained in the visions will not emerge until the day comes.
Paul spoke of some of these things which will be in play during the period when he explained to the early Thessalonian believers that the events of the Day of the Lord were not in process in their day. They thought that they had missed the gathering of the Lord's "harpazo" [immortalization action of believers] and were troubled because there was false teaching that the Day of the Lord had already begun. Paul would say the same thing today because the beginning of the time frame of the Day of the Lord is still pending.
The emergence of the lawless one, the little horn king of the northern Middle East, and his following will not come into view by those on the earth until the Day of the Lord begins. The beginning of this time frame will come suddenly, without expectation, and with an extreme shaking of the earth felt by all humans on the planet. At the same time Satan and the fallen angelics will be forced to the earth and the 10 horns and the little horn will emerge among them in the Middle East, and they will be overtly visible exactly as they are described in the prophetic visions. It is these who will attack and destroy Mystery Babylon's [the unbelieving world] great city in one day which will occur in the early part of the time frame of the 70th week described in Daniel’s visions. At the same time Satan will be allowed to open the abyss and to release his "antichrist" who will then proceed to engage the little horn and his 10 kings.
The little horn will gain a massive following, primarily composed of the inhabitants of the Middle East, and these will worship him as a god. He will demonstrate great super natural powers far beyond human capabilities and will be able to defeat all human opposition against his ambitions. This human little horn [king] will front Satan and his "antichrist" Abaddon-Apollyon, the angelic king of the abyss. Nothing will stop this man of lawlessness. He will destroy the great city of the Gentiles, conquer all of the Middle East, and destroy much of the opposition forces against his stronghold who will contend with him from the south, the east, and the north. These nations will come from outside of the Middle East proper and he will utterly sweep them away by destroying their invading armies and possibly their nations.
He will also have at his disposal the fallen angelics who will be activated upon the earth and these forces will be employed to the task of eliminating humans who will not follow him. Satan will attempt to rule the earth through his beast from the abyss, his false prophet, the little horn and his human followers, and his contingent of fallen angelics. His objective will be to prevent the Lord's coming millennial kingdom on the earth by establishing his own. The Lord will remove restraint and allow his folly, but will cut it short and will destroy Satan's plan at the battle of Armageddon during the 30 days immediately following the end of the 2,520 day 70th week. The little horn will reach his objective of control over the Middle East and will cause great destruction across the planet. By midweek he will have also entered and conquered Israel and will add Jerusalem, the temple mount, and nation to his Middle Eastern kingdom. He will then rule for 42 months [second 1,260 days of the 70th week].
All of this will not come into play until the 70th week begins ….. the beginning of the Day of the Lord. It is the Lord who will control and direct this process for His purposes. These will include His judgment of an unbelieving world, meeting the 6 objectives for a believing remnant part of national Israel recorded in Daniel 9, and the establishment of His own millennial kingdom on the earth. This time frame of His millennial rule will be an extension of His "Day". This total time frame will include revealing Himself to the world, drawing Satan to the earth for his defeat, eliminating billions of human unbelievers from the planet, and establishing His kingdom of believing mortals who will survive the tribulations of the 70th week. He will rule the earth from Jerusalem for 1,000 years and Satan will be kept from interacting with the mortal nations that will develop during the period.
The period of the Day of the Lord will continue beyond His millennial kingdom into the endless time frame of eternity. Satan will be released at the end of the Lord's earthly kingdom and he will cause another human rebellion. The Lord will quickly vanquish this aggression by destroying Satan and by renovating the earth and universe with fire. Then the human spirits [the tares] of all unbelievers will be eliminated and all believers [the wheat] will possess immortality and will enter His eternity.