It is quite clear that in Daniel 4-5 the character of Nebuchadnezzar replaces a more original Nabonidus, who was the historical father of Belshazzar. The tale in ch. 4 is a less historical adaptation of the story in the Prayer of Nabonidus (4Q242), with rather extensive parallels existing between the two stories. The affliction is due to a divine פתגמ in both texts (פִּתְגָמָ֔א in Daniel 4:17, פתגם א[להא in 4Q242). The affliction lasts a period of 7 years or times (cf. the use of “time” to refer to a year in 12:7), in contrast to the 10 years Nabonidus gives in his own autobiographical account of his withdrawal (NABON H 1-2). Nabonidus in 4Q242 worshipped “gods of silver and gold, [bronze, iron], wood, stone, clay”, a phrase that finds a very close parallel in Daniel 5:4 (“gods of gold, silver, bronze, iron, wood, and stone”). The affliction is reversed through the intervention of an exiled Jew who tells the king to submit to God. The Jewish diviner instructs Nabonidus to “write and proclaim” his confession and in the 4Q242, the king writes his confession in the first person, “I, Nabonidus, was smitten with a bad disease”, etc. In Daniel 4, Nebuchadnezzar writes a letter to “all peoples” stating his faith in “the Most High God” (cf. 3:32-33), and which describes his experience in the first person, “I, Nebuchadnezzar, was at ease in my palace” (4:1), “I, Nebuchadnezzar, lifted my eyes to heaven” (4:31), etc. In both cases, the king’s decree praising the Most High includes a first-person account of his affliction. This is unusual and can hardly be a coincidence. The biblical story has close literary links to 4Q242 but the latter is at the same time more primitive: it pertains to an episode known independently from historical sources (whereas no such episode is known for Nebuchadnezzar’s reign in any contemporary source), it gives the correct name of the king and location in Teima, and the Jewish diviner is not yet identified with Daniel.
The narrative that follows in Daniel 5 alludes to the affliction story in 5:20-21 and states that Belshazzar is the son of the king that was humbled by God (5:22). Historically Belshazzar was indeed the son of Nabonidus. The simplest explanation then is that the story originally concerned Nabonidus (with roots in his historical withdrawal from Babylon) but the author of Daniel replaced him with the much-better known Nebuchadnezzar. The emphasis is on a father-son relationship; “Nebuchadnezzar, your father” (v. 18; cf. v. 2, 11) is paired with “you, Belshazzar, his son” (v. 22), it is the queen mother herself who reminds Belshazzar about things that had happened in the days of “your father” (v. 11) — which is meaningless with respect to the historical Belshazzar since he was a co-regent with his father Nabonidus — with the queen mother reinforcing the family connection between Nebuchadnezzar and Belshazzar, and Daniel chides Belshazzar for repeating the mistakes of his father. The most natural way to read the text is to accept it at face value as stating that Belshazzar was Nebuchadnezzar’s son; it is special pleading to appeal to a more unusual reading of the text to save the story from historical inaccuracy. When Belshazzar was officially called “son of the king” in contemporary texts, the reference was to the father-son relationship between Belshazzar and Nabonidus, not Nebuchadnezzar. Also the real queen mother, Adda-Guppi, who was Nabonidus’ mother and Belshazzar’s grandmother, who had been alive during the reign of Nebuchadnezzar, died in 547 BCE – some years prior to the fall of Babylon. Nabonidus’ own father was Nusku-balassu-iqbi, not Nebuchanezzar, and the god Nusku had his cult center in Harran, so likely he was a local Assyrian official of Harran and not a Chaldean. And there was no historical “third year of Belshazzar” (Daniel 8:1). This was a construct of the author of Daniel. Belshazzar was never king in his own right and he governed Babylon mainly in the middle of Nabonidus’ reign when he was away from Babylon, c. 553–543 BCE. This is the period when Belshazzar “son of the king” is mentioned in dated business tablets.
As for Darius the Mede, the author was working from an unhistorical sequence of kings (Nebuchadnezzar > Belshazzar > Darius the Mede > Cyrus the Persian), with a Median kingdom inserted in between the Babylonian and Persian kingdoms. In the OG version, there was another Median king between Belshazzar and Cyrus (with Xerxes the Mede ruling between Belshazzar and Darius). The author here is working with a Hellenistic four kingdom schema popular in this period which reckoned the kingdoms as Assyria > Media > Persia > Macedonia/Greece. Historically, the Median empire was contemporaneous with the Neo-Babylonian kingdom and it was Cyrus, not Darius, who brought the Neo-Babylonian period to a close. The author of Daniel has replaced “Assyria” with “Babylon” because it was the latter that exiled the Jews but this created a historical problem because Media was conquered by Persia before the Neo-Babylonian period came to an end. The author is likely confusing Cyrus’ conquest of Babylon in 539 BCE (which for the Chronicler ended Jeremiah’s 70 years) with the later conquest of Babylon in 522-521 BCE by Darius the Great who waged war against the city and defeated Nebuchadnezzar IV (who like Nebuchadnezzar III attempted to revive the Neo-Babylonian kingdom). It was this event that probably led to the return of Zerubabbel and Joshua son of Jozedek from exile (520 BCE) and the rebuilding of the Temple (completed in 515 BCE), and this Darius reorganized his empire in satrapies as described in Daniel 5. This detail rules out identifying Darius with any number of minor figures such as governors of Babylon. Darius was depicted as ruling over Babylon directly and ruling over a vast empire of 127 satrapies (6:2), which were only appointed after the fall of Babylon, and this recalls both the 20 satrapies organized by the historical Darius the Great and the 127 satrapies of Esther 1:1 that span from Ethiopia to India. Thus Darius was not depicted as a co-regent or ruling over a small kingdom or the province of Babylon, and he is portrayed as ruling prior to Cyrus the Persian (6:29; cf. 6:28 OG: “King Darius was gathered to his fathers and Cyrus the Persian succeeded to his kingdom”). Contemporary documents show incontrovertibly that Cyrus ruled over his empire as monarch after the fall of Babylon in 539 BCE instead of Darius the Mede who is never mentioned in administrative and business tablets. The author of Daniel knew that the Persian empire followed that of the Medes, but did not realize that the conquest of Media by the Persians occurred prior to the fall of Babylon. For more on this vein, I would recommend H. H. Rowley’s Darius the Mede and the Four World Empires in the Book of Daniel (University of Wales, 1964)
http://www.moellerhaus.com/70week.htm

Premillenial Interpretations do Violence to the Prophecy The following diagram illustrates the way that some interpreters force the scripture into their interpretation instead of diagramming the scripture and fitting the interpretation to the scripture. Such a forced interpretation as that illustrated below could not be done by our Omniscient God, He would not create a freak to represent what is real. Imagine a god who said that “History will look like a statue” and then to match the interpretation you have to draw toes as long as the rest of the statue. Such a statue has to lie on his side because he can not stand on such deformed feet. Since premillenial scholars know that the division of the Roman Empire into 10 kingdoms took place about 500 years after the advent of Jesus of Nazareth and they err in not believing “the little stone” has hit the image in the feet as yet, then they are forced to draw toes that are 1500 years long. The diagram is not actually proportionate however since an honest picture of the toes make them 1 and 1/3 times longer that the complete standing image. The rest of the statue is proportionate to the time periods that each symbolic portion predicted. Surely God did not predict history represented by a freak statue.