Complex sentence: The Élysée has gardens, in which presidents hosted parties on the afternoon of Bastille Day until 2010, since Nicolas Sarkozy, the former President of France, decided to stop organizing this event because of France's high debt and the economic crisis.
Split into simpler sentences: The Élysée has gardens, in which presidents hosted parties on the afternoon of Bastille Day until 2010. Since then, Nicolas Sarkozy, the former President of France, decided to stop organizing this event because of France's high debt and the economic crisis.