Daniel 8:12 "And an host

People of God coming from all tribes and nations

was given him

Rome now turning into Papal Rome

against the daily sacrifice

or daily ministry of Jesus

by reason of transgression

mixing paganism with christianity,

and it cast down the truth to the ground; and it practised, and prospered."

I've heard the host called the Church or God's People, many of them must of come from The Barbarian Tribes.
I believe the Barbarian Tribes were part of this Host, but was it Satan that split up Rome or God?
I'm going to say it was Satan. This is about mixing Paganism with Christianity.
Here are a few quotes from Ellen White that kinda say that.

What was the origin of the great apostasy? How did the church first depart from the simplicity of the gospel? By conforming to the practices of paganism, to facilitate the acceptance of Christianity by the heathen. The apostle Paul declared, even in his day, "The mystery of iniquity doth already work." 2 Thessalonians 2:7. During the lives of the apostles the church remained comparatively pure. But "toward the latter end of the second century most of the churches assumed a new form; the first simplicity disappeared, and insensibly, as the old disciples retired to their graves, their children, along with new converts, ... came forward and new-modeled the cause." Robert Robinson, Ecclesiastical Researches, ch. 6, par. 17, p. 51. To secure converts, the exalted standard of the Christian faith was lowered, and as the result "a pagan flood, flowing into the church, carried with it its customs, practices, and idols." Gavazzi, Lectures, page 278. As the Christian religion secured the favor and support of secular rulers, it was nominally accepted by multitudes; but while in appearance Christians, many "remained in substance pagans, especially worshiping in secret their idols." Ibid., page 278. {GC 384.5}

Has not the same process been repeated in nearly every church calling itself Protestant? As the founders, those who possessed the true spirit of reform, pass away, their descendants come forward and "new-model the cause." While blindly clinging to the creed of their fathers and refusing to accept any truth in advance of what they saw, the children of the reformers depart widely from their example of humility, self-denial, and renunciation of the world. Thus "the first simplicity disappears." A worldly flood, flowing into the church, carries "with it its customs, practices, and idols." {GC 385.1}

The advancing centuries witnessed a constant increase of error in the doctrines put forth from Rome. Even before the establishment of the papacy, the teachings of heathen philosophers had received attention and exerted an influence in the church. Many who professed conversion still clung to the tenets of their pagan philosophy, and not only continued its study themselves, but urged it upon others as a means of extending their influence among the heathen. {GC 58.2}

But there is no union between the Prince of light and the prince of darkness, and there can be no union between their followers. When Christians consented to unite with those who were but half converted from paganism, they entered upon a path which led farther and farther from the truth. Satan exulted that he had succeeded in deceiving so large a number of the followers of Christ. He then brought his power to bear more fully upon them, and inspired them to persecute those who remained true to God. None could so well understand how to oppose the true Christian faith as could those who had once been its defenders; and these apostate Christians, uniting with their half-pagan companions, directed their warfare against the most essential features of the doctrines of Christ. {4SP 45.2}

Then the Lord sent them messages of encouragement, declaring that He would deliver them from their captivity and restore them to His favor. It was this that Satan was determined to prevent. A remnant of Israel had already returned to their own land, and Satan was seeking to move upon the heathen nations, who were his agents, to utterly destroy them. {2TT 170.2}

Satan numbers the world as his subjects, he has gained control of the apostate churches; but here is a little company that are resisting his supremacy. If he could blot them from the earth, his triumph would be complete. As he influenced the heathen nations to destroy Israel, so in the near future he will stir up the wicked powers of earth to destroy the people of God. {LDE 256.1}