We believe that the loud cry of the third angel began in 1888 at the conference in Minneapolis with the message of “Christ Our Righteousness.” That was the beginning of the “light” of the angel of Revelation 18:1-4.
Revelation 18:1-4 –

“The time of test is just upon us, for the loud cry of the third angel has already begun in the revelation of the righteousness of Christ, the sin-pardoning Redeemer. This is the beginning of the light of the angel whose glory shall fill the whole earth.” -(The Review and Herald, November 22, 1892Selected Messages, vol. 1, p. 363.

“Christ our Righteousness” “is the message that God commanded to be given to the world. It is the third angel’s message, which is to be proclaimed with a loud voice, and attended with the outpouring of His Spirit in a large measure.” – Testimonies to Ministers and Gospel Workers, p. 92.

While the proclamation of the third angel’s message swells to a loud cry, another angel comes to join this work.

“The angel who unites in the proclamation of the third angel’s message is to lighten the whole earth with his glory. A work of worldwide extent and unwonted power is here foretold.”

“The work will be similar to that of the Day of Pentecost. As the ‘former rain’ was given, in the outpouring of the Holy Spirit at the opening of the gospel, to cause the upspringing of the precious seed, so the ‘latter rain’ will be given at its close for the ripening of the harvest.” – The Great Controversy, p. 611.

>Many did not accept the message of “Christ Our Righteousness,” and this had grave consequences. When the First World War (1914-1918) broke out, there arose a severe crisis. The fourth and sixth commandments were openly violated; but some members remained faithful to the Ten Commandments and, being guided by the Spirit of the Lord, carried forward a work of reformation simultaneously in various countries.

In fact, it is the faithful, or the prophesied remnant of Revelation 12:17; 14:12 and 3:14-22, whom God will use at the close of His work to give the last warning message to the world.
Revelation 12:17 – And the dragon was wroth with the woman, and went to make war with the remnant of her seed, which keep the commandments of God, and have the testimony of Jesus Christ.
Revelation 14:12 – 
Here is the patience of the saints: here are they that keep the commandments of God, and the faith of Jesus. 
Revelation 3:14-22
 – And unto the angel of the church of the Laodiceans write; These things saith the Amen, the faithful and true witness, the beginning of the creation of God; I know thy works, that thou art neither cold nor hot: I would thou wert cold or hot. So then because thou art lukewarm, and neither cold nor hot, I will spue thee out of my mouth. Because thou sayest, I am rich, and increased with goods, and have need of nothing; and knowest not that thou art wretched, and miserable, and poor, and blind, and naked: I counsel thee to buy of me gold tried in the fire, that thou mayest be rich; and white raiment, that thou mayest be clothed, and that the shame of thy nakedness do not appear; and anoint thine eyes with eyesalve, that thou mayest see. As many as I love, I rebuke and chasten: be zealous therefore, and repent. Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me. To him that overcometh will I grant to sit with me in my throne, even as I also overcame, and am set down with my Father in his throne. He that hath an ear, let him hear what the Spirit saith unto the churches.

“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; and it will accomplish its work.”

“But God still has a people in Babylon; and before the visitation of His judgments these faithful ones must be called out, that they partake not of her sins and ‘receive not of her plagues.’ Hence the movement symbolized by the angel coming down from heaven, lightening the earth with his glory and crying mightily with a strong voice, announcing the sins of Babylon. In connection with his message the call is heard: ‘Come out of her, My people.’ These announcements, uniting with the third angel’s message, constitute the final warning to be given to the inhabitants of the earth.” – The Great Controversy, pp. 390, 604.