In the night of 28/29th July 1914 the first shots of the First World War were fired by the Austro-Hungarian army (K.u.K. army) on the city of Belgrade, the capital of the Kingdom of Serbia. The afternoon before (on the 28th July) the Austro-Hungarian empire had declared war on Serbia via a telegram (see here). It was during that night that the first military and civilian victims of the First World War fell: the 16 year old Dušan Đonović, a military volunteer fell on Serbian side and on the Austro-Hungarian side the first victims reported were Karl Eberling, the captain of the first tug and his helmsman, Mikhail Gemsberger. Other (Serbian) sources mention Ištvan Balohi as the first fallen K.u.K. soldier .
Unfortunately, there are claims that the first victims and soldiers fell on the West front. For example the “Historisch Nieuwblad” (=a Dutch magazine about history)) wrote that André Peugeot (from France) and Albert Mayer (from Germany) were the first victims of the First World War: they died on 2nd August 1914 (see here and the article here). Of course, this is not true as many sources wrote about the first WWI victims which fell during the first days of WWI on the Serbian / Austro-Hungarian front. Not only this Dutch magazine is failing in indicating the first victims of WWI, many others do as well.
It is estimated that the Kingdom of Serbia alone lost more than 1.1 million inhabitants during the war (both army and civilian losses), which represented over 26% of its then total population and 58% of its adult male population.
Seen the above mentioned fact about the first victims (soldiers & civilians) of the First World War mentioned by several sources from several countries it is clear that the first scarifies were made on the Serbian – Austro-Hungarian front during the first days of WWI and not on the West front.
 Serbia and the Balkan front, 1914 -the Outbreak of the Great War-, James Lyon ,
ISBN 978-1-4725-8004-7, page 96-7.
 According to the article from Blic (Serbian), 11/11/2016: link
 According to the article “Sudnji rat” by Čedomir Antić in the Serbian newspaper Politika, 13/09/2008: link
My earlier blogs about WWI:
Site about Serbian WWI soldiers who died in the Netherlands: www.secanje.nl