Civilian casualty ratio
Some 7 million combatants on both sides are estimated to have died during World War I, along with an estimated 10 million non-combatants, including 6.6 million civilians. The civilian casualty ratio in this estimate would be about 59%. Boris Urlanis notes a lack of data on civilian losses in the Ottoman Empire, but estimates 8.6 million military killed and dead and 6 million civilians killed and dead in the other warring countries. The civilian casualty ratio in this estimate would be about 42%. Most of the civilian fatalities were due to famine, typhus, or Spanish flu rather than combat action. The relatively low ratio of civilian casualties in this war is due to the fact that the front lines on the main battlefront, the Western Front, were static for most of the war, so that civilians were able to avoid the combat zones.
Allies of World War I
The exact role played by Serbian officials in the assassination of Archduke Franz Ferdinand is still debated but despite complying with most of their demands, Austria-Hungary invaded on 28 July 1914. While Serbia successfully repulsed the Austro-Hungarian army in 1914, it was exhausted by the two Balkan Wars and unable to replace its losses of men and equipment. In 1915, Bulgaria joined the Central Powers and by the end of the year, a combined Bulgar-Austrian-German army occupied most of Serbia. Between 1914-1918, Serbia suffered the greatest proportional losses of any combatant, with over 25% of all those mobilised becoming casualties; including civilians and deaths from disease, over 1.2 million died, nearly 30% of the entire population.