Understanding the “70 years”.
The “people of the land” was a political group that was strong enough to install kings Josiah and Jehoahaz. All held an anti-Egyptian stance.
Later, Nebuchadnezzar removed just the Jewish leadership of the cities but he left the “people of the land” behind.
The Jewish priestly group, now in captivity, sought an explanation for their plight. God had promised this land to Abraham, but the power now resided with a foreign king. The city’s power brokers, the intelligentsia, had been removed. Only the "people of the land" remained in Judea.
These exiled priests explained that their current predicament resulted from the people failing to heed the priests and prophets sent by God (that is, themselves).
So while they were in Babylon, they (the Judahites) wrote or rewrote their history from their own theocratic viewpoint, producing propaganda that framed their history according to their religious viewpoint. Thus in particular Deuteronomy, Joshua, Judges and 1 & 2 Kings were written (or rewritten) for their own immediate contemporaries to explain their predicament. Little wonder they expressed a poor opinion of the Israelite kings. It is likely these exiled priests influenced other writings, including Jeremiah and parts of Isaiah.
I believe the Judahites saw the exile of the Israelites and of themselves (“all Israel”) as a single unit. They said that the loss sustained by each group of clans resulted from the same cause – their disobedience to God as proclaimed by the priests and prophets. The priests wanted to regain the position of power they had enjoyed. Have a look at the extremist behaviour and demands for sectarian purity made by Ezra, especially his hatred towards the “people of the land”, claiming they had desecrated the nation’s purity by marrying wives from other nations while the leadership had been exiled.
According to these religionist historians, the Captivity was forewarned for centuries, not by a single statement from Jeremiah. He uttered an unconditional declaration, not a prophecy, that Babylon would be dominant for 70 years. He later pleaded for the city (with its priestly power base) to be saved from destruction, but when the people rebelled against the decree of continued servitude to Babylon, this was the final straw.
Prophecy is conditional; God would have restored the Israelites had they repented. Likewise with the condition of Judah (and Benjamin, of course), their return was conditional upon them calling upon God and confessing their sin.
After “THE” 70 years of Babylon’s rule had ended, Daniel was concerned that the sanctuary still remained desolate. When Daniel understood that Jeremiah said God demanded wholesale confession, Daniel fell to his knees, confessing the people’s sin, as he faced the city that was the subject of his prayer.
But the ongoing struggle between the priestly class and the “people of the land” who had remained behind ensured the sanctuary was not restored until decades after Babylon’s seventy years of dominance had ended. The "people of the land" fought bitterly to prevent the priestly class regaining the power they once held.
The Jewish writers thus saw the destruction of the city and its temple as the result of centuries of disobedience to God as proclaimed by them, not due to any prophecy by Jeremiah. They understood that the 70 years referred to the period of Babylon’s dominance.
