Complex sentence: Oxfordians also observe Shakespeare set almost half of his plays in France and Italy and filled them with local details that were not strictly necessary-details, Oxfordians believe, that could only have been obtained by personal experiences.
Split into simpler sentences: Oxfordians also observe Shakespeare set almost half of his plays in France and Italy and filled them with local details that were not strictly necessary. These details, Oxfordians believe, that could only have been obtained by personal experiences.