On page 60 of Prelude to Israel’s Past, Niels Peter Lemche states:
“Clearly, the Old Testament consciously connects Yahweh with southern Palestine, indicating the originality of the information contained in these narratives. These historical kernels in the Exodus narratives suggest that either the Israelites lived in southern Palestine or Midianites (according to other biblical information, the Kenites) brought the worship of Yahweh to Palestine. Consequently, Yahwism spread throughout the region until finally Yahweh became Israel’s national God. In support of such a theory, scholars refer to the evidence that Moses’ father-in-law was either a Midianite or a Kenite.”
Moses in the Book of Exodus was tending the flocks of Midianites when he encountered YHWH at Horeb, and there are second millennium B.C.E. Egyptian documents that refer to an area called “Shasu Yahweh”, which (on the basis of Egyptian sources) Lemche locates that at the Sinai desert. Those are reasons that Lemche traces Yahwism to the South. Moreover, while Lemche states on pages 51-52 that Moses could have been invented, he still thinks that the Moses story reflects something historical: that the Israelites got Yahwism from the Midianites or the Kenites.