Complex sentence: In 1190, after leaving England on the Third Crusade, Richard appointed Otto Earl of York, but the authenticity of this grant was doubted by the men of Yorkshire and Otto never took possession of his earldom.
Split into simpler sentences: In 1190, after he left England to join the Third Crusade, Richard appointed Otto Earl of York. The authenticity (or authority) of this grant was doubted by the vassals of Yorkshire, who prevented Otto taking possession of his earldom.