Complex sentence: In the late 1980s conspiracy theories that vilified the Roman Catholic Church began to become widespread and were supported by Serbian publishers, this was of particular significance since these were attacks on the national religion of the Croats.
Split into simpler sentences: In the late 1980s, conspiracy theories that vilified the Roman Catholic Church began to become widespread and were supported by Serbian publishers. This was of particular significance since these were attacks on the national religion of the Croats.