Complex sentence: The queen dowager's rule was not to be peaceful; the first to rise against her, in 1383, was John of Palisna, Ban of Croatia, who was mainly opposed to the centralizing policy which her husband had enforced.
Split into simpler sentences: The queen dowager's rule was not to be peaceful. The first to rise against Elizabeth, in 1383, was John of Palisna, Ban of Croatia, who was mainly opposed to the centralizing policy which her husband had enforced.