The Neapolitan War was a conflict between the Napoleonic Kingdom of Naples and the Austrian Empire. It started on 15 March 1815 when Joachim Murat declared war on Austria and ended on 20 May 1815 with the signing of the Treaty of Casalanza. The war occurred during the Hundred Days between Napoleon's return from exile and before he left Paris to be decisively defeated at the Battle of Waterloo. The war was triggered by a pro-Napoleon uprising in Naples, and ended after a decisive Austrian victory at the Battle of Tolentino and Ferdinand IV was reinstated as King of Naples and Sicily. However, the intervention by Austria caused resentment in Italy, which further spurred on the drive towards Italian unification.