Complex sentence: The Kingdom of Italy was born on 17 March 1805 when the "Italian Republic", whose president was Napoleon, became "Kingdom of Italy", with Napoleon as King of Italy and Eugène de Beauharnais viceroy.
Split into simpler sentences: The Kingdom of Italy was born on 17 March 1805. On that day, the "Italian Republic", whose president was Napoleon, become "Kingdom of Italy", with Napoleon as King of Italy and Eugène de Beauharnais viceroy.