Complex sentence: Upon taking over the family Medici bank from his father, Piero had a financial overview prepared; the results led him to call up a number of long-standing loans, many to various Medici supporters, which his father had let stand.
Split into simpler sentences: Upon taking over the family Medici bank from his father, Piero had a financial overview prepared. The results led him to call up a number of long-standing loans, many to various Medici supporters, which his father had let stand.