Are there any non Jews believing in Judaism?

The religion Judaism is not believed by non Israelis. It is true that Judaism was a religion in Ethiopia and may be in Russia, Europe, USA, etc. But those believers of Judaism in Ethiopia claim they are Israelis in race and it is said that these people have the seal of David (Israeli flag) on their hand as tattoo. Are there any non Jews people believing in Judaism?

It is true that Hinduism is believed by Indians and Buddhism by Chinese and few peripheral areas peoples. What makes Judaism different from Hinduism and Buddhism is that it is first preached in the Middle East just as Christianity and Islam. While Christianity and Islam have spread in many nations irrespective of racial identity, Judaism did not.

What is the reason?  Is it because the Jews did not like to preach Judaism to other races because of their beliefs and values that they are the only chosen people and Zionism values? Or was Judaism accepted by non Jews before Christianity and Islam and that it has been vanished by Christianity and Islam? If this is the case, why did not Christianity vanished by Islamic spread?