history - Were there any other religions before Judaism that their followers should convert to Judaism?

You could imagine that with the advent of a new religion, any followers of the last religion would be required to convert to the new religion.

Which followers of which religion converted to Judaism, when Judaism came on the scene?

How did they know that they had to convert to Judaism?

Answer

Rashi, BeReishis 12:5 says that Avraham and Sarah converted people to Judaism. The religion that was around before that time was paganism, as is known.