Ruby,
There is no doubt that monotheism became the dominant form as an outcome of the Neo-Babylonian Captivity and Exile. As one clear example, consider Deutero-Isaiah (ch 40ff), which were written at that time.
Prior to that, the nation was monolatrous, not monotheistic. Some apply the term henotheistoc. All of these terms would be foreign to them. They were created in recent centuries.
Study the evolution from the god named EL, who appears for example in Genesis 1. There are several serious books and scholarly articles that explain the way that the Israelites took a war-god named Yahweh and over time they assimilated the features of other Gods, such as EL, creating a very different Yahweh.
For example, they took the pantheon of gods from EL and passed them onto Yahweh. Initially, EL was the creator God, but that was given to Yahweh. EL was the "Ancient of Days", and so on and on.
EL and his pantheon came from the northern neighbours. Yahweh was not one of those northern gods. Instead, he came to the Israelites from the south with Moses.
Doug