Yahwism

Yahwism was the religion of ancient Israel, centered around a god named Yahweh. Yahweh was one of many gods and goddesses of the pantheon of gods of the Land of Canaan, the southern portion of which would later come to be called the Land of Israel. Yahwism existed parallel to Canaanite polytheism, and in turn it was the monolatristic, primitive predecessor stage of modern-day Judaism, in its evolution into a monotheistic religion.
Despite the fact that modern Judaism and Yahwism are both based on the veneration of Yahweh, there are clear distinctions between the two belief systems. Unlike the religions that would descend from it, Yahwism was characterized by henotheism/monolatrism, which recognized Yahweh as the national god of Israel, but nevertheless did not explicitly deny the existence of other gods of ancient Semitic religion, such as Baal, Asherah, and Astarte — though this did not always allow their individual worship in conjunction to Yahweh.
The exact transition between what is now considered monolatristic Yahwism and monotheistic Judaism is somewhat unclear, however it is evident that the event began with radical religious amendments such as the testaments of Elijah and the reforms of Hezekiah and Josiah and they had all been fulfilled by the end of the Babylonian captivity, when the recognition of Yahweh as the sole god of the universe had finally secured a majority of the Jewish people (see Deutero-Isaiah). Some scholars believe that monolatry was also encouraged by religious reforms of David during the United Monarchy; however, the United Monarchy and the actions of David are a subject of heavy debate among archaeologists and biblical scholars.
History.
The centre of ancient Israel's religion through most of the monarchic period was the worship of a god named Yahweh, and for this reason the religion of Israel is often referred to as Yahwism. Yahweh, however, was not the original god of Israel; it is El, the head of the Canaanite pantheon, whose name forms the basis of the name "Israel", and none of the Old Testament patriarchs, the tribes of Israel, the Judges, or the earliest monarchs, have a Yahwistic name (i.e., one incorporating the name of Yahweh). It is unclear how, where, or why Yahweh appeared in the Levant; even his name is a point of confusion. The exact date of this occurrence is also ambiguous: the term "Israel" first enters historical records in the 13th century BCE with the Merneptah Stele, and while the worship of Yahweh is circumstantially attested to as early as the 12th century BCE, there is no attestation or record of even Yahweh's name, let alone his origin or character, until more than five-hundred years later, with the Mesha Stele (9th century BCE).
Most historians see Israel emerging in the hill country of Palestine in the late Bronze/early Iron ages circa 1200 BCE (an arbitrary date with which archaeologists mark the division between these two ages), and many, while cautioning that the Hebrew Bible/Old Testament is not necessarily a reliable guide, believe that the shared religion of Yahweh played a role in this emergence. This early Israel was a society of rural villages, but in time urban centers grew up and society became more structured and more complex, and in the 9th century BCE Israel was founded as a kingdom with its capital at Samaria. 
After the 10th century BCE the tribes and chiefdoms of Iron Age I were replaced by ethnic nation states. In each kingdom, the king was also the head of the national religion and thus the viceroy on Earth of the national god. In Jerusalem this was reflected each year when the king presided over a ceremony at which Yahweh was enthroned in the Holy Temple. The Hebrew Bible gives the impression that the Jerusalem Temple was always meant to be the central, or even sole, temple of Yahweh, but this was not the case. The earliest known Israelite place of worship is a 12th-century open-air altar in the hills of Samaria featuring a bronze bull reminiscent of Canaanite "Bull-El" (El in the form of a bull), and the archaeological remains of further temples have been found at Dan on Israel's northern border and at Arad in the Negev and Beersheba, both in the territory of Judah. Shiloh, Bethel, Gilgal, Mizpah, Ramah, and Dan were also major sites for festivals, sacrifices, vow-making, private rituals, and the adjudication of legal disputes.
During an era of religious syncretism, it became accepted among the Israelite people to consider the Canaanite god El as the same as Yahweh. This is arguably the beginning of the end for Yahwism and the very beginnings of Judaism. Indeed, as this idea became prevalent in the Jewish people's religion, El soon was thought to have always been the same deity as Yahweh, as evidenced by Exodus ,
The worship of Yahweh alone began at the earliest with prophet Elijah in the 9th century BCE, and at the latest with prophet Hosea in the 8th; even then it remained the concern of a small party before gaining ascendancy in the exilic and early post-exilic period. The early supporters of this faction are widely regarded as being monolatrists rather than true monotheists, as instead of believing that Yahweh was the only god in existence, they instead believed that he was the only god the people of Israel should worship, a noticeable departure from the traditional beliefs of the Israelites, nonetheless. It was during the national crisis of the Babylonian Exile that the followers of Yahweh went a step further and finally outright denied that the other deities aside from Yahweh even existed, thus marking the transition from monolatrism to true monotheism, and from Yahwism to Judaism. Certain scholars date the start of widespread monotheism to 8th century BCE, and view it as a response to Neo-Assyrian aggression.
Worship of Baal and Yahweh coexisted in the early period of Israel's history, but they were considered irreconcilable after the 9th century BCE, following the efforts of King Ahab and his queen Jezebel to elevate Baal to the status of national god, although the cult of Baal did continue for some time.
Beliefs and practices.
Pantheon.
There is a broad consensus among modern scholars that the religion of the Israelites prior to the Babylonian exile was basically polytheistic, involving a plethora of gods and goddesses. Heading the pantheon was 
Yahweh, whose role as the supreme god of Israel is confirmed by such external evidence as the preponderance of Yahwistic names on personal seals from the late 8th to the 6th centuries BCE. Alongside Yahweh was his consort Asherah, although at the 5th century Jewish colony at Elephantine in Egypt, Yahweh's consort was seen as the Egyptian goddess Anat, and the goddess "Anat-Yahu" was worshiped in the settlement's temple. Various biblical passages indicate that statues of Asherah were kept in Yahweh's temples in Jerusalem, Bethel, and Samaria. 
Below Yahweh and Asherah were second tier gods and goddesses such as Baal, Shamash and Yareah (these two, found in the second level of the pantheon throughout the West Semitic world, are addressed directly in Joshua 10:12), Mot the god of death (who appears in Hosea and Jeremiah as a deity who would punish Judah for its sins on Yahweh's behalf), and the goddess Astarte, all of whom had their own priests and prophets and numbered royalty among their devotees. A goddess called the "Queen of Heaven" was also worshiped: she was probably a fusion of Astarte and the Mesopotamian goddess Ishtar, although the phrase is possibly a title of Asherah.
A third tier was made up of specialist deities such as the god of snakebite-cures - his name is unknown, as the biblical text identifies him only as Nehushtan, a pun based on the shape of his representation and the metal of which it was made - and below these again was a fourth and final group of minor divine beings such as the "mal'ak", the messengers of the higher gods, who in later times became the angels of Christianity, Judaism and Islam.
The idea that Yahweh alone should be worshiped began at the earliest with the 9th century prophet Elijah and more probably with Hosea in the 8th; it remained the concern only of small groups opposed to the mainstream except for a brief period when it was championed by King Josiah, but triumphed in the exilic and early post-exilic periods.
Worship.
The practices of Yahwism were largely characteristic of other Semitic religions of the time, including festivals, sacrifices, vow-making, private rituals, and the adjudication of legal disputes. The center of Yahweh-worship lay in three great annual festivals coinciding with major events in rural life: Passover with the birthing of lambs, Shavuot with the cereal harvest, and Sukkot with the fruit harvest. They became linked to events in the national mythos of Israel: Passover with the exodus from Egypt, Shavuot with the law-giving at Sinai, and Sukkot with the wilderness wanderings. The festivals thus celebrated Yahweh's salvation of Israel and Israel's status as his holy people, although the earlier agricultural meaning was not entirely lost.
Animal sacrifices played a big role in Yahwism and Judaism (prior to the destruction of the Second Temple in 70 CE) on altars, with the subsequent burning and the sprinkling of their blood, a practice described in the Bible as a daily Temple ritual for the Jewish people. Sacrifice was presumably complemented by the singing or recital of psalms, but the details are scant. The rituals detailed in Leviticus 1–16, with their stress on purity and atonement, were actually followed only after the Babylonian exile and the Yahwism/Judaism transition. In reality, any head of a family was able to offer sacrifice as occasion demanded. Prayer itself played little role in practice. 
Yahwism was famously aniconic, meaning that Yahweh was not depicted by a statue or other image. Yahweh's throne on the mercy seat of the Ark of the Covenant is described as two "cherubim" forming the seat and a box as a footstool, while the throne itself was empty. This is not to say that Yahweh was not represented in some symbolic form, and early Israelite worship probably focused on standing stones. No satisfactory explanation of Israelite aniconism has been advanced, and a number of recent scholars have argued that Yahweh was in fact represented prior to the reforms of Hezekiah and Josiah late in the monarchic period: to quote one recent study, "early aniconism, "de facto" or otherwise, is purely a projection of the post-exilic imagination".
In addition to the sacrificial priests, a great role in Yahwism, and still later Judaism, were played by prophets and epic heroes, reflected in the modern Jewish texts by legends about Samson and Joshua. Worship was performed on literal high places, with the Jerusalem Temple sitting on Mount Moriah/Mount Zion (hence, the Temple Mount), and the Samaritans' temple sitting on Mount Gerizim, although this may just be more of a coincidence than an intentional practice. Talismans and the mysterious "teraphim" were also probably used. It is also possible Yahwism employed ecstatic cultic rituals (compare the biblical tale of David dancing naked before the Ark of the Covenant) at times where they became popular, and potentially, according to some scholars, even human sacrifice.
Later amendments to Yahwistic practice are difficult to qualify, as there is an unclear scholarly consensus on what explicitly connotes "Judaism" vs. Yahwism during the generally accepted "transition period" of the Babylonian captivity. According to Biblical scholar Yehezkel Kaufmann, “The exile is the watershed. With the exile, the religion of Israel comes to an end and Judaism begins.”