Complex sentence: The King's desire to marry a woman with two living ex-husbands threatened to cause a constitutional crisis in the United Kingdom and the Dominions, and ultimately led to the King's abdication in December 1936 to marry "the woman I love".
Split into simpler sentences: The King's desire to marry a woman with two living ex-husbands threatened to cause a constitutional crisis in the United Kingdom and the Dominions. This prospect ultimately led to the King's abdication in December 1936 to marry "the woman I love".