The year 605 BC is the true political background of Daniel 1.
The battle of Carchemish is its main military turning point. The Babylonian victory causes Egypt to retreat and opens to Nebuchadnezzar the possibility of extending his authority over Syria-Palestine.
Judah, until then under Egyptian domination, then gradually enters the Babylonian sphere.
Daniel 1 places in this new situation the intervention against Jerusalem, the transfer of certain Temple vessels, and the presence in Babylon of Daniel and his companions.
This first phase must nevertheless be distinguished from the later catastrophes.
605 BC marks the beginning of Babylonian domination; 597 BC corresponds to a much larger deportation; 586 BC marks the destruction of Jerusalem and the Temple.
This distinction helps us understand the historical progression of the biblical narrative.
It also allows us to grasp the full significance of Daniel 1. The book does not begin after the complete disappearance of Judah, but at the moment when the political order of the Near East shifts and the young Daniel is swept up in the consequences of this transformation.
The story of Daniel thus begins with the rise of Babylon. It will continue long enough for the same Daniel to be still present when this empire in turn disappears.