San Marino Declares War on Austria-Hungary
While Italy declared war on Austria-Hungary on 23 May 1915, San Marino remained neutral.
Italy, suspecting that San Marino could harbour Austrian spies who could be given access to its new radiotelegraph station, tried to forcefully establish a detachment of Carabinieri on its territory and then suspended any telephone connections with the Republic when it did not comply.
Two groups of 10 volunteers each did join Italian forces in the fighting on the Italian front, the first as combatants and the second as a medical corps operating a Red Cross field hospital. It was the presence of this hospital that later caused Austrian authorities to suspend diplomatic relations with San Marino.
Although propagandistic articles appeared in the New York Times as early as 4 June 1915 claiming that San Marino declared war on Austria-Hungary, the republic never entered the war.
The history of San Marino is both very European and typical for the Italian Peninsula, and yet helps explain its unusual characteristics as the sole remaining Italian city-state.
San Marino is the only surviving Italian city-state. Like Andorra, Liechtenstein and Monaco, it appears an anachronism, a reminder of the times when Europe — particularly Germany, Italy and the Pyrenees — was made up of tiny political units, sometimes extending no further than a cannon could fire from a city’s walls. Along with Vatican City it is one of the two states completely surrounded by a single other country in Europe. San Marino proudly asserts its independence and various treaties of friendship have been signed with Italy since the latter’s unification.
Wikipedia: History Of San Marino
Wikipedia: World War I