Complex sentence: Assimilation, however, was met by anti-Semitism in Europe and split into a competing non-assimilationist diaspora nationalism, known as Zionism, with which and where all Jews might realize a secure and separate national religious identity.
Split into simpler sentences: Assimilation, however, was met by anti-Semitism in Europe. It split into a competing non-assimilationist diaspora nationalism, known as Zionism, in the belief that all Jews might realize a secure and separate national religious identity.