What people were the first to willingly accept the idea of worshiping only one god?

Answer 1

The first continuous monotheistic tradition and religion as we know it, was and is Judaism, the tradition founded by Abraham. It began 3800 years ago, and its founding principle is that God is One. This was well before the Egyptian king Akhenaten, who in any case (according to tradition) was influenced by Israelite beliefs.
As far as Zoroastrianism is concerned, there is no consensus on when Zoroaster lived. Also, the Talmud (Sanhedrin 39a) states that Zoroastrianism has two gods.

Answer 2

Muslims

Muslims believe that the main principle of Islam " worshipping one God who is Allah, the Lord of all creations " is not a new principle.

Muslims believe that all prophets came to the people with this principle as a priority of their task in conveying the message of Allah. All of them called the people for worshipping, submission & subordination to one God who is Allah, the Creator of everything.

Probably the first monotheistic religions was Zoroastrianism. Zoroastrianism is the name given to the religion and beliefs based on the teachings which are attributed to the Persian religious leader Zararthushtra ( in Greek Zoroaster, in later Persian Zartosht). Zoroastrianism was founded somewhere around 1200BCE. This date is based on changes in the language from the common tongue spoken by the Proto-Iranians and the Proto-Aryans.

The Gathas and the chapter known as Yasna Haptanghaiti are all written in Old Avestan Old Avestan and Vedic Sanskrit are both descendants of the Proto-Indo-Iranian language and the Gathic Old Avestan is still quite close in structure to the Sanskrit of the Rig-Veda in language usage. However the Sanskrit of the Rig-Veda is somewhat more conservative in outlook and structure than the Avestan of the Gathas and so, based on the changes in the languages, scholars date the Gathas to around 1000 BCE, give or take a couple of centuries.

** But note also that the issue lies with how old is the Rig Veda, which no one seems to know with anything approximating certainty. There are also those who think the Gathas are older than the Rig Veda, Dastur Dhalla, and some other linguists see the Gaathic language as more complex and archaic. Most of what we know about Zoroaster comes to us from a variety of sources, the Avesta, the Gathas, Greek historical works, archaeological evidence and oral history.

Answer 3

1) According to careful research, the original tradition, which was widespread, was monotheistic. However, it died out completely in a relatively brief span of time. This belief does not refer to a specific people, country, or named religion, since it was not centralized or organized.
2a) The first continuous monotheistic tradition and religion as we know it, was and is Judaism, the tradition founded by Abraham. It began 3800 years ago, and its founding principle is that God is One. This was well before the Egyptian king Akhenaten, who in any case (according to tradition) was influenced by Israelite beliefs.

2b) Some might claim that monotheistic Judaism started later, as (for example) King Josiah made reforms in the late First Temple period. However, this is the view of secular academe, and flies in the face of tradition. Judaism had already been monotheistic for eight centuries by the time of Josiah. All he did was to eradicate the traces of the idolatrous influences of those Jews who had strayed from their own religion. This had happened repeatedly (such as with Jehoshaphat [2 Chronicles 17:6], and Samuel before him [1 Samuel 7:3-4]); and those who strayed into pagan practices never encompassed the entire people.

3) Zoroastrianism, which might be suggested as another early contender, is not such a clear matter. There is no consensus on when Zoroaster lived. Moreover, the Zoroastrians believed in two gods, not one. The Jewish Sages who redacted the Talmud in the early centuries of the Common Era lived in Babylonia, witnessed the practices of the Zoroastrians, and recorded this fact (Talmud, Sanhedrin 39a). In addition, in Zoroastrianism:

• there is worship through intermediaries, who are themselves "worthy of worship"
• evil and good each has its own creator
• some of its adherents believe in a self-creating universe
• some modern scholars see it as a form of pantheism.

Answer 4

The first continuous monotheistic tradition and religion as we know it, was and is Judaism, the tradition founded by Abraham. It began 3800 years ago, and its founding principle is that God is One. This was well before the Egyptian king Akhenaten, who in any case (according to tradition) was influenced by Israelite beliefs.

• Link: How Abraham founded Judaism
  

Some might claim that monotheistic Judaism started later, as (for example) King Josiah made reforms in the late First Temple period. However, Judaism had already been monotheistic for eight centuries by the time of Josiah. All he did was to eradicate the idolatrous influences of those Jews who had strayed from their own religion. This had happened repeatedly (such as with Jehoshaphat [2 Chronicles 17:6], and Samuel before him [1 Samuel 7:3-4]); and those who strayed into pagan practices never encompassed the entire people.

• Link: Were the Israelites monotheistic
  

Zoroastrianism, which might be suggested as another early contender, is not such a clear matter. There is no consensus on when Zoroaster lived. Moreover, the Zoroastrians believed in two gods, not one. The Jewish Sages who collated the Talmud in the early centuries of the Common Era lived in Babylonia, witnessed the practices of the Zoroastrians, and recorded this fact (Talmud, Sanhedrin 39a). In addition, in Zoroastrianism:

• there is worship through intermediaries, who are themselves "worthy of worship"
• evil and good each has its own creator
• some of its adherents believe in a self-creating universe
• some modern scholars see it as a form of pantheism.

See also the other Related Links.

Link: What exactly did Josiah do?

Link: What do Jews believe about God?

Answer 5

Adam and his wife, peace be upon them both.