At the time of the interpretation, our footnotes would not have existed, if that makes sense. Yes, there was an understanding at the time that the statue in the king's dream represented several kingdoms--beginning with Nebuchadnezzar's "head of gold" (2:38), which was directly stated by Daniel. But, did anyone know to what kingdoms the rest of the body referred? Not at the time. What's challenging about prophecy is that fulfillment details are not always provided, so you have to live through the times before hindsight fills in the footnotes. Then, it becomes history! But, it does make prophecy open to interpretation/s, and that makes reading passages like this challenging.
Thankfully, we now have tools like study Bibles, with footnotes and column notes, commentaries, the Internet and, yes, history books, to help confirm a direction if not the actual facts. Would everyone like to know more about Revelation? You bet! Are there multiple interpretations out there--because we probably haven't lived through all of those times yet to know what all those references mean [but it depends on your interpretation]? Bottom line: Do NOT lose heart over prophetic writings because you don't fully understand them. God did mean those words for people at the time (as a warning, often, and as a sign of His presence and foreknowledge), and as we live--and look to reliable, Biblically based experts and resources--God will reveal the significance of His message to us in our time.
This will not be the last time we see references to these four earthly kingdoms in Daniel. They will take a different form in Chapter 7. (Hey, now you know what's coming up!) These four kingdoms are important to reflect upon in terms of the history of the Jewish church.
"This image [of the statue] represented the kingdoms of the earth that should successively bear rule among the nations and have influence on the affairs of the Jewish church. The four monarchies were not represented by four distinct statues, but by one image, because they were all of one and the same spirit and genius, and all more or less against the church. It was the same power, only lodged in four different nations, the two former lying eastward of Judea, the two latter westward."
Then, there's the stone "...cut out of a mountain without hands...." (2:45) This represents Christ in His second coming--the Millennial kingdom. My commentaries and study Bible lead me back to look at Psalm 118: 22-23, from which Jesus Himself quotes in Matthew 21:
"The stone which the builders rejected,
This became the chief corner stone;
This came about from the Lord,
And it is marvelous in our eyes."
What else could possibly topple down the strongest of earthly kingdoms? Only that which God would build. The Messiah, "the stone" may have been "rejected," but he would become "the chief corner stone" at the hand of God. Could Nebuchadnezzar have imagined such a kingdom? We do not know, here, what exactly Nebuchadnezzar thought about the interpretation of his dream. But we do know how he responded to Daniel:
"The king answered Daniel and said, 'Surely your God is a God of gods and a Lord of kings and a revealer of mysteries, since you have been able to reveal this mystery.'" (2:47)
Not only does he respond with his words, but the king treats Daniel like, well, a king!
"It was the custom of the country by prostration to give honour to kings, because they have something of a divine power in them (I have said, You are gods); and therefore this king, who had often received such veneration from others, now paid the like to Daniel, whom he supposed to have in him a divine knowledge, which he was so struck with an admiration of that he could not contain himself, but forgot both that Daniel was a man and that himself was a king."
"Then the king promoted Daniel and gave him many great gifts, and he made him ruler over the whole province of Babylon and chief prefect over all the wise men of Babylon. And Daniel made request of the king, and he appointed Shadrach, Meshach and Abed-nego over the administration of the province of Babylon, while Daniel was at the king’s court." (2:48, 49)
A couple of things to note about the ending to this chapter. Daniel "made request" of the king. In a time when he could have lorded over the kingdom and his countrymen his new status and gifts, he continues to honor the king and to serve in his court. Respecting his office, Daniel seeks and receives permission from the king to bring his friends into positions of administration.
[Digression: Maybe you saw a footnote in your Bible about Daniel's use of his friends' new Babylonian names instead of using their Jewish names. Chapter 2 is partially written in Hebrew and partially written in Aramaic. Part of God's plan for His word to reach the Jews (in Hebrew) and the Gentiles (in Aramaic). The Gentiles would know the three by their Babylonian names. Would you say that's true for you?]
"Those that helped him with their prayers shall share with him in his honours, such a grateful sense had he even of that service. The preferring of them would be a great stay and help to Daniel in his place and business. And these pious Jews, being thus preferred in Babylon, had great opportunity of serving their brethren in captivity, and of doing them many good offices, which no doubt they were ready to do. Thus, sometimes, before God brings his people into trouble, he prepares it, that it may be easy to them."--Matthew Henry
Did you catch that last sentence? We might just revisit that idea as we embrace Daniel 3 on Monday.