Was Deuteronomy written early or late after Moses' death?
The background and setting of the book reflect conditions prior to the conquest of Canaan under Joshua. There is no mention of a king in Judah or of the city of Jerusalem, which is mentioned over one hundred times by the prophet Jeremiah (who wrote in Josiah's day). It is unlikely that a sixth-century author would make no allusion whatever to that capital city or its temple. The twelve tribes are represented as one nation (instead of, as in Josiah's period, the kingdoms of Judah and Israel). The Transjordan cities of refuge are named, while those in Canaan (which were named later by Joshua) are not. The Babylonian names of months are not used, and there are no Persian loan words in the vocabulary, even though such words would be expected to appear in a work supposedly written during a period when these empires were dominant. Moses, Aaron, and Joshua are named, but no later persons or later historical incidents are mentioned. It is unlikely that a later author, even one well-versed in the lore of the past, could so completely avoid the use of later terms and the mention of persons and events of his own period.
Perhaps most significant is the general conformity of Deuteronomy's structure to the covenant or treaty form of the mid-second millennium B.C. (the approximate time of Moses). We find the following treaty elements in Deuteronomy: (a) a preamble identifying the covenant mediator (Deut. 1:1–5); (b) a historical prologue reviewing previous covenant history (Deut. 1:6–4:40); (c) stipulations expounding the covenant way of life (Deut. 4:44–11:32; 12–26); (d) a declaration of sanctions stating the blessings for obedience and curses for disobedience of the covenant (Deut. 27–30); and (e) a provision for the administration of the covenant after the death of the inaugural mediator (Deut. 31–34). The main divisions from the covenant documents of Moses' lifetime, then, are discernible in the fifth book of the Pentateuch, Deuteronomy.
We conclude, therefore, that Deuteronomy was written by Moses, Israel's lawgiver, before his death in 1406 B.C.