Complex sentence: Once again, the incumbent president was a Whig who had succeeded to the presidency upon the death of his war-hero predecessor; in this case, it was Millard Fillmore who followed General Zachary Taylor.
Split into simpler sentences: Once again, the incumbent president was a Whig who had succeeded to the presidency upon the death of his war-hero predecessor. In this case, it was Millard Fillmore who followed General Zachary Taylor.