Some of the most prominent communists were secular, ethnic Jews. This did not stop antisemitism from remaining in the former Russian empire or even prevented it from showing up in the Communist Party. Added on to the antisemitism was fear of religious Jews (religion contrasted with atheistic communism) and Zionism (which contrasted with Soviet nationalism). It was decided to give the Jews their own homeland in order to ensure secular communist principles and offer an alternative to Zionism. No established homeland wanted to give up a piece of their territory to the Jews, though. Western Russia and Ukraine were the centers of Judaism in the USSR but no where did they make a majority. No Orthodox peasant town and no secular city wanted to be given to a Jewish homeland. So in 1934 in the Far East along the Chinese border the Jewish Autonomous Region (JAR) was established as an outpost of European communism in an Asian land.
Stalin's Zion was to be a beacon of ethnic Jewish communism. Yiddish was declared the offical language and the government started a massive propaganda campaign to convince Jews to move to the JAR. Cities like Valdeym and Amurzet were founded while the preexisting settlement Birobidzhan became the capital. Newspapers, preforming arts, and a university were established to create a new culture.
At the high point Jews made up only a third of the population in JAR. Stalin's purges, World War II, and just not wanting to live in a place which is swampy in the summer and is Siberia in the winter prevented the large Jewish migration that was hoped for. In 1948 (between two of Stalin pruges) Israel was established and Zionism defeated Communism in appealing to the Jewish masses. The second purge in the 1950s destroyed many of the Yiddish landmarks and most of the Jews fled or were "dealt" with.
Today the Jewish population of the Jewish Autonomous Oblast is less than two percent officially (some estimates have it up to fifteen percent with people hiding their Jewish identities). The region is mixed with Russians making an overwhelming majority but the rest is a mixture of former Soviet subjects and Chinese. A sort of revival is going on with the Jewish population there as a new synagogue built in 2004 and schools are offering Yiddish again. The Israeli government is even offering cultural aide to help the revival.
It is questionable whether or not the Jewish Autonomous Region stood a chance. The success of Israel, physical geography, and Stalin's monstrous nature doomed it. It is an oddity today but it is a part of history and should not be forgotten.
For more information check out the official English-language website of the Jewish Autonomous Region.