Complex sentence: The Count of Flanders ruled an "immensely wealthy state" that had traditionally led an autonomous existence on the edge of the French state; the French king was generally regarded as having suzerainty over Flanders, but under former monarchs the relationship had become strained.
Split into simpler sentences: The Count of Flanders ruled an "immensely wealthy state" that had traditionally led an autonomous existence on the edge of the French state. The French king was generally regarded as having suzerainty over Flanders, but under former monarchs the relationship had become strained.