Answer: Sardinia mobilised its army on 9 March 1859. Austria mobilised on 9 April 1859 and issued an ultimatum on 23 April demanding the complete demobilisation of the Sardinian Army. When it was not heeded, Austria started a war against Sardinia on 26 April. The first French troops entered Piedmont on 25 April, and France declared war on Austria on 3 May.
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