Daniel 5:19-24
Daniel 5:19
And for the majesty that he gave him, all people, nations, and languages, trembled and feared before him: whom he would he slew; and whom he would he kept alive; and whom he would he set up; and whom he would he put down.
The size of Babylon and the way they had attacked and conquered other nations had brought fear into those he conquered.  It was up to the king and his officers to make a decision who would remain alive and who would pose a threat to the kingdom.  Those who were deemed threats would be executed but those who could add something to the kingdom would be kept alive, just as Daniel and his three companions were kept alive because they were well educated and showed promise.  There was also the decision to keep puppet kings in places that were conquered.  Thee puppets would pay a tribute to Babylon which would help increase their wealth.  It was for these reasons that the people would fear being conquered because they never knew their fate until they were actually captured.
Daniel 5:20
But when his heart was lifted up, and his mind hardened in pride, he was deposed from his kingly throne, and they took his glory from him:
Daniel continues to tell Belshazzar that at the height of his power, Nebuchadnezzar had made a fatal mistake, and that was, he became puffed up with pride and as a result God had to deal with him.  God took him from his throne and removed his glory as the king.  All the people that saw Nebuchadnezzar every day in his splendor and majesty would now see him as a deposed king with no authority.
Daniel 5:21
And he was driven from the sons of men; and his heart was made like the beasts, and his dwelling was with the wild asses: they fed him with grass like oxen, and his body was wet with the dew of heaven; till he knew that the most high God ruled in the kingdom of men, and that he appointeth over it whomsoever he will.
The same rulers in the kingdom who saw Nebuchadnezzar as a mighty king were now seeing him as no better than a grass eating animal.  That remained for a period of seven years until all the pride that was in him was removed and he acknowledged that God was the one who gave kingdoms to whomever He wished plus it was He who was the real ruler in every kingdom in the world.  The kingdom of Heaven always ruled the kingdoms of earth and that still continues today.
Daniel 5:22
And thou his son, O Belshazzar, hast not humbled thine heart, though thou knewest all this;
Belshazzar was the grandson of Nebuchadnezzar and all the things which happened to him was known by him.  He may have been a much younger man but he knew the things which befell his grandfather so he could not claim ignorance in the matter.  Belshazzar followed in the footsteps of his grandfather exalting himself with all pride and arrogance and was about to pay the ultimate penalty for that sin against God.
Daniel 5:23
But hast lifted up thyself against the Lord of heaven; and they have brought the vessels of his house before thee, and thou, and thy lords, thy wives, and thy concubines, have drunk wine in them; and thou hast praised the gods of silver, and gold, of brass, iron, wood, and stone, which see not, nor hear, nor know: and the God in whose hand thy breath is, and whose are all thy ways, hast thou not glorified:
Daniel now lays out the indictment of Belshazzar.  He has lifted himself up in pride and arrogance which was against the God of Heaven.  He challenged God by bringing out all the holy vessels which Nebuchadnezzar brought back to Babylon from the Temple in Jerusalem.   He defiled them by allowing his guests to drink wine in them for the purpose of becoming drunk at their orgy.  In conjunction with the drinking they did, they were worshipping the false gods of Babylon no doubt paying homage to them while in a drunken state.  Daniel reminds him that those false gods cannot hear, see, or know anything because they simply are creations of man and are represented by carved figures.  Daniel then tells him that the real God who holds his next breath and his life was not being glorified.  Probably while the Temple utensils were being defiled, there was probably blaspheming of God going on.  Since they had the holy utensils, then things were probably said about the God of Israel, which he would now have to pay the ultimate penalty for.
Psalm 135:15-18 (KJV)   The idols of the heathen are silver and gold, the work of men's hands.  {16} They have mouths, but they speak not; eyes have they, but they see not;  {17} They have ears, but they hear not; neither is there any breath in their mouths.  {18} They that make them are like unto them: so is every one that trusteth in them.
Habakkuk 2:18-19 (KJV)   What profiteth the graven image that the maker thereof hath graven it; the molten image, and a teacher of lies, that the maker of his work trusteth therein, to make dumb idols?  {19} Woe unto him that saith to the wood, Awake; to the dumb stone, Arise, it shall teach! Behold, it is laid over with gold and silver, and there is no breath at all in the midst of it.
Daniel 5:24
Then was the part of the hand sent from him; and this writing was written.
Now since the vessels of the Temple in Jerusalem were being defiled, God now sent a judgment upon Belshazzar as He did to Nebuchadnezzar.  The finger of God wrote on the wall in the presence of all.  Just as the vessels were defiled by all, now all would see the judgment of God.