Judaism itself is one religion; the religion of Judaism. See also:
Divisions within Judaism
Yes. Dictionaries define "Judaism" as The monotheistic religion of the Jews, since the founding principle of Judaism was and is the belief in One God. This was the teaching which was spread by Abraham, and has continued since then. From Judaism, belief in One God has spread through the Western world.See also the Related Links. Link: A biography of Abraham
Link: What do Jews believe about God?
1) As the Jewish communities spread and move. This phenomenon was set in motion by the various expulsions and persecutions, which drove Jewish populations to settle in new places. 2) As non-Jews come in contact with Jews, there is a degree of influence upon them. Ancient writers speak of large numbers of people in the Mediterranean area who had taken on various Jewish practices. It was these semi-converts who were especially likely to adopt Christianity.
See also the Related Links.
Link: The diaspora
Link: The influence of Hebrew traditions on the Western world
Why a Jew goes to a synagogue?This is where the Jews worship and its just like asking a christian why they go to church; and its simple - to worship their God in their own way and how they feel comfortable worshiping because if they didn't feel comfy then what is the point in worshiping there?
Public prayer services are part of halakha (Jewish law) and tradition (Talmud, Berakhot 26a). Prayer is an important form of communicating with God, and maintaining a relationship with Him; and it is also good for the health of the soul, to which Torah, prayer and religious observances are a form of nourishment.
Check out the link below (from the Hebrew Wikipedia).