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.