"There has long been one very good reason to consider dating Deuteronomy far earlier than the seventh century, and to the second millennium BCE: certain core elements of the book seem to be based on treaty forms most similar to the Hittite treaties known from the fourteenth and thirteenth centuries BCE. That Deuteronomy relies on the form of a treaty is another well-established consensus position in biblical scholarship."
Sep 14, 2014
The Dating of Deuteronomy and the Suzerain-Vassal Treaty Forms
I think that too much is often made of the similarities between the suzerain-vassal treaty forms and the books of Torah, most notably Deuteronomy. But whatever the similarities exist between Deuteronomy and the treaty forms seem to better fit the extant second millennium forms rather than the much later Neo-Assyrian forms. If correct, this supports a much earlier date of composition for Deuteronomy than is typically held in critical scholarship. So I think that Aaron Koller is spot on in his article "Deuteronomy and Hittite Treaties" in Bible and Interpretation here. See the abstract below but make sure to read the article.