Complex sentence: Two modern churches developed from the schism, the Chaldean Church, which entered into communion with Rome as an Eastern Catholic Church, and the Assyrian Church of the East, the followers of these two churches are almost exclusively ethnic Assyrians.
Split into simpler sentences: Two modern churches developed from the schism, the Chaldean Church, which entered into communion with Rome as an Eastern Catholic Church, and the Assyrian Church of the East. The followers of these two churches are almost exclusively ethnic Assyrians.