This is a very complicated topic that is full of popular speculation, which I exemplify below. My understanding is that there is no one underlying cause for Judaism's "transition" into monotheism (and that it is debatable itself, that "Judaism" was ever polytheistic by technicality), however there are interesting texts and major influences that may be worth looking into.

There are many suppositions and a lot of conjecture about Judaism's (specifically its antecedent, ancient Israelite religions) pre-monotheistic history (i.e. in its polytheistic/henotheistic discipline) and where it mostly derives its influences.

On the topic of popular speculation, look at the topic of Yahweh (Jehova) and Asherah, for instance. You might have heard of Yahweh's consort Asherah, who was arguably relevant in the picture of the early religion. Though historically speaking, the idea of Asherah and her role is mostly speculative (specifically in regards to her equitability to Yahweh at the time), there are occasions about Asherah and her role that makes her a popular speculative representation about early "Judaism's" (or rather, Yahwist) world of "henotheism/polytheism."

A second important primary source for YHWH's status in Judah is one of the Khirbet el-Qom inscriptions dating between 800-750 BCE. It mentions "YHWH and his Asherah," indicating that Judah's supreme god YHWH had a paredra ("sacred consort"). This indication of the cult of Asherah as paredra of YHWH can be connected with the HB references to the cult of the "Queen of Heaven" in Jerusalem.

Herbert Niehr, "The Rise of YHWH in Judahite and Israelite Religion: Methodological and Religio-Historical Aspects" from The Triumph of Elohim: From Yahisms to Judaisms by Diana Vikander Edelman

This is a popular example of one of the surmises that treads on the line of oversimplification and hyperbole, that is simply speculative and conjectural.

On the subject of monotheism, and in relevance to /u/darkekniggit's question, "Follow up. Is there anything known about the precursor faiths to Judaism if there are any?"

This is where ancient Iran's Zoroastrianism, and ancient Egypt's Akhenaten play a part.

I would read about Zoroastrianism's influence on Judaism's monotheism here. (Kaufmann Kohler, A. V. W. Jackson. "Zoroastrianism.") (Also, you should read this post about Zoroastrianism and its relevance to Judaism.)

Other general posts which cover this topic are this and this.