Complex sentence: The various Basque provinces generally regarded their "fueros" as tantamount to a constitution, a view that has been accepted by others, including President of the United States John Adams, who cited the Biscayan "fueros" as a precedent for the United States Constitution.
Split into simpler sentences: The various Basque provinces generally regarded their "fueros" as tantamount to a constitution, a view that was accepted by some others, including President of the United States John Adams. He cited the Biscayan "fueros" as a precedent for the United States Constitution.