Why is it called Deuteronomic history?

Another answer from our community:

The Deuteronomic History is named by the developers of the documentary hypothesis in the 19th century to refer to the history also written by the author of Deuteronomy. They gave this history a separate name because they believed it represented a different perspective of a different author who wrote much later than the time of Moses.

This is connected with their second major presupposition, that of an evolutionary development of the religion of Israel from primitive polytheism (many gods) to Henotheism (many gods, with one chief god) to Monotheism (one God). Josiah's reform was intended to bring the 'triumph of Monotheism' by attributing its authority to antiquity, whereas it was the invention of a much alter age.

Thus although the theory is elaborate it has no supporting evidence except its own internal circular reasoning. There never was any evidence of any kind for the theory as postulated, except in the minds of its creators and proponents. No documents of any kind exist which support the proposed deuteronomic history or the existence of the alleged author. No corroborating historical detail external to The Bible itself, supports it. The internal witness of the Bible itself, also thoroughly refutes this history.

Thus there never was such a thing as the Deuteronomic History as postulated by the documentary theorists. Nor was there a necessity to create such a history. I believe the evidence points toward a single author in the time-frame suggested by the text itself, around 1400 BC, that person being Moses.