Judaism, as are many non-missionary religions, was historically geographically based. It originated in the area of Mesopotamia and the Fertile Crescent, in the area of present day Israel which is considered the Jewish homeland. Although many people have converted to the religion over time, and those who were traditionally Jewish were forced to leave their ancestral homeland in the diaspora, it is primarily practiced by persons of Semitic origin, and conversion is actively discouraged. Persons of Semitic origin have distinct physical features which often distinguish them from others, and since they are quite frequently (but not always) Jewish, it is easy to blur the line of distinction between Semitic ethnicity and religious identity. In fact, persons who oppose Jewish ideas or Jewish believers are often called "anti-Semitic," an unfortunate term.
Judaism is first and last a religion. A substantial number of those who practice the religion are ethnically Semitic. This fact, however, does not morph those who practice the religion into a race or ethnic group.