In Revelation 18 an Angel gives the 'Loud Cry' and Babylon is described in detail and the call made to come out of her, and the warning given that "God hath remembered her iniquities."

Revelation 18:1-5
1 And after these things I saw another angel come down from heaven, having great power; and the earth was lightened with his glory.
2 And he cried mightily with a strong voice, saying, Babylon the great is fallen, is fallen, and is become the habitation of devils, and the hold of every foul spirit, and a cage of every unclean and hateful bird.
3 For all nations have drunk of the wine of the wrath of her fornication, and the kings of the earth have committed fornication with her, and the merchants of the earth are waxed rich through the abundance of her delicacies.
4 And I heard another voice from heaven, saying, Come out of her, my people, that ye be not partakers of her sins, and that ye receive not of her plagues.
5 For her sins have reached unto heaven, and God hath remembered her iniquities.

We see the angel cry "mightily with a strong voice", and "the earth was lightened with his glory." Here is pictured the final announcement of the fall and demon possession of Babylon, accompanied by the divine call, "Come out of her, My people." The separation from Babylon is necessary in order to be emancipated from her sins and to escape her plagues.

The time of the loud cry is definitely located. It comes just before the close of probation and the falling of the seven last plagues, in which "is filled up the wrath of God." With a loud c ry or strong voice the call is given for God's people remaining in the religious organizations constituting Babylon to separate from what has "become the habitation of devils, and the hold of every foul spirit, and the cage of every unclean and hateful bird." Babylon includes the mother and the large family of daughters, all of whom have fallen and been taken possession of by Satanic agencies.

The loud cry is the final message of salvation during the outpouring of the Holy Spirit as prophesized in the last days, a call which will bring every human being to a final and irrevocable decision. The latter rain furnishes the power so that the message can be quickly finished and bring any of Gods people out of Babylon.

It is evident that the purpose of the loud cry is to call out of Babylon all who had not previously made the separation. This must be done before probation closes and the plagues fall. The Lord designates those called out as "My people" to escape from Babylon, a doomed spiritual entity which is followed in wonder by the world.

Why the great urgency to come out and separate from it, because Babylon has become completely possessed and controlled by satanic forces, has fallen to an all-time low level of spiritual life, and is clearly a unfitting dwelling place for the people of God. The sins of Babylon, like the tower of Babel in ancient Babylon, have piled up until they have "reached unto heaven, and God hath remembered their iniquities." Just as the angels hurried Lot and his family out of the doomed city of Sodom before its destruction, so the saints of God must be hastened out of the final spiritual city of destruction before the wrath divine brings it to a deserved end.

When Peter wrote his first epistle, he concluded by saying, "The church that is in Babylon, elected together with you, saluteth you" (1 Peter 5:13, KJV). In the Roman Catholic Douay Version of the Bible, the footnote to this verse says, 'Babylon. Figuratively Rome.' During the Protestant Reformation all leaders taught essentially the same, from Luther, in 1520, onward. These men were scattered over Germany, Switzerland, France, and England. In Britain were men like William Tyndale, Bishops Ridley and Hooper, Archbishop Cranmer, Bishops Bale, Jewell, and Coverdale, and John Knox and others. Bishops Ridley's farewell letter before his martyrdom, in 1555, repeatedly referred to "Babylon," and called for separation from Rome. We see the rise of the woman on the scarlet-colored beast which is Babylon, clearly the Papacy, the doomed spiritual entity that Gods people must come out of.

When Pagan Rome fell, the rise of Papal Rome was more of a transition into a religious-political government and is the woman riding a scarlet-colored beast, and prophecy tells us the Roman Catholic Church moves on until end with the kings of the earth committing fornication with her, but her doom is coming.

Today we see the kings and leaders, and the world, looking more and more to the Pope for guidance in national and religious affairs. It is this mixing of the two that allows the advance the church's authority and develops the fornication of the kings or world powers with the church.

The system with political and monetary side has not fallen although the religious and spiritual side is dead or dying for the most part, you can see it in the empty Cathedrals and Catholic churches. But the daughter churches also are going to suffer as they continue its practices and joining its call for ecumenism to unite the world under its lead and its goal of a united world religion under head, the Pope, which we see them slowly drifting towards.

We see the complete sequence given in Revelation 14...
Revelation 14:6-11
6 And I saw another angel fly in the midst of heaven, having the everlasting gospel to preach unto them that dwell on the earth, and to every nation, and kindred, and tongue, and people,
7 Saying with a loud voice, Fear God, and give glory to him; for the hour of his judgment is come: and worship him that made heaven, and earth, and the sea, and the fountains of waters.
8 And there followed another angel, saying, Babylon is fallen, is fallen, that great city, because she made all nations drink of the wine of the wrath of her fornication.
9 And the third angel followed them, saying with a loud voice, If any man worship the beast and his image, and receive his mark in his forehead, or in his hand,
10 The same shall drink of the wine of the wrath of God, which is poured out without mixture into the cup of his indignation; and he shall be tormented with fire and brimstone in the presence of the holy angels, and in the presence of the Lamb:
11 And the smoke of their torment ascendeth up for ever and ever: and they have no rest day nor night, who worship the beast and his image, and whosoever receiveth the mark of his name.

So what is the prophecy about, well here is a good description on it..
'In the eighteenth chapter of the Revelation the people of God are called upon to come out of Babylon. According to this scripture, many of God's people must still be in Babylon. And in what religious bodies are the greater part of the followers of Christ now to
be found? Without doubt, in the various churches professing the Protestant faith.--GC 383 (1911).

Notwithstanding the spiritual darkness and alienation from God that exist in the churches which constitute Babylon, the great body of Christ's true followers are still to be found in their communion.--GC 390 (1911).

Babylon's Fall Not Yet Complete​
"She made all nations drink of the wine of the wrath of her fornication" (Rev. 14:6-8). How is this done? By forcing men to accept a spurious sabbath.--8T 94 (1904).

Not yet, however, can it be said that . . . "she made all nations drink of the wine of the wrath of her fornication." She has not yet made all nations do this. . . . Not until this condition shall be reached, and the union of the church with the world shall be fully accomplished throughout Christendom, will the fall of Babylon be complete. The change is a progressive one, and the perfect fulfilment of Revelation 14:8 is yet future.--GC 389, 390 (1911).

When do her sins reach unto heaven [Rev. 18:2-5]? When the law of God is finally made void by legislation.--ST June 12, 1893.

God's Last Warning Message​
God has given the messages of Revelation 14 their place in the line of prophecy and their work is not to cease
till the close of this earth's history.--EGW'88 804 (1890).

Revelation 18 points to the time when, as the result of rejecting the threefold warning of Revelation 14:6-12, the church will have fully reached the condition foretold by the second angel, and the people of God still in Babylon will be called upon to separate from her communion. This message is the last that will ever be given to the world.--GC 390 (1911).

[Rev. 18:1, 2, 4, quoted.] This scripture points forward to a time when the announcement of the fall of Babylon, as made by the second angel of Revelation 14 (verse 8), is to be repeated, with the additional mention of the corruptions which have been entering the various organisations that constitute Babylon, since that message was first given, in the summer of 1844. . . . These announcements, uniting with the third angel's message, constitute the final warning to be given to the inhabitants of the earth. . . .

The sins of Babylon will be laid open. The fearful results of enforcing the observances of the church by civil authority, the inroads of spiritualism, the stealthy but rapid progress of the papal power--all will be unmasked. By these solemn warnings the people will be stirred. Thousands upon thousands will listen who have never heard words like these.--GC 603, 604, 606 (1911).

So what does it point to, its clear its a religious-political power, a image of the original and we see it forming today, and SOP gives even more on it...

'But today in the religious world there are multitudes who, as they believe, are working for the establishment of the kingdom of Christ as an earthly and temporal dominion. They desire to make our Lord the ruler of the kingdoms of this world, the ruler in its courts and camps, its legislative halls, its palaces and market places. They expect Him to rule through legal enactments, enforced by human authority.

Since Christ is not now here in person, they themselves will undertake to act in His stead, to execute the laws of His kingdom. The
establishment of such a kingdom is what the Jews desired in the days of Christ. They would have received Jesus, had He been willing to establish a temporal dominion, to enforce what they regarded as the laws of God, and to make them the expositors of His will and the agents of His authority. But He said, "My kingdom is not of this world." John 18:36. He would not accept the earthly throne. {DA 509.2}

Protestant churches that have followed in the steps of Rome by forming alliance with worldly powers have manifested a similar desire to restrict liberty of conscience. In the seventeenth century thousands of non-conformist ministers suffered under the rule of the Church of England. Persecution always follows religious favoritism on the part of secular governments. {4SP 277.2} Rev.
18:3,9-24.

The Protestant churches, having received doctrines that the Word of God condemns, will bring these to the front and force them upon the consciences of the people, just as the papal authorities urged their dogmas upon the advocates of truth in Luther?s time. The same battle is again to be fought, and every soul will be called upon to decide upon which side of the controversy he or she will be found. {CTr 323.5}

"Babylon has been fostering poisonous doctrines, the wine of error. This wine of error is made up of false doctrines, such as the natural immortality of the soul, the eternal torment of the wicked, the denial of the pre-existence of Christ prior to His birth in Bethlehem, and advocating and exalting the first day of the week above God's holy and sanctified day. These and kindred errors..." TM 61.3. also GC 389, 586.

The great city is divided into three parts; that is, the three grand divisions of the false and apostate religions of the world (the great city),
Paganism, Catholicism, and relapsed Protestantism, seem to be set apart each to receive its appropriate doom. The cities of the nations fall; universal desolation spreads over the earth; every island flees away, and the mountains are not found; and great Babylon comes in remembrance before God. Read her judgments, as more fully described in chapter 18. {1897 UrS, DAR 653.4}