More than 9 million soldiers died in the Great War of 1914 - 1918, now more commonly known as World War One. This represents 13% of the 70 million or so personnel who were mobilised in this major war which was centred in Europe. All the world's great powers were involved, with Britain, France and Russia making up the Allies on one side; and the Central Powers of Germany and Austria-Hungary on the opposing side.
According to war veterans records ww1, the Allies lost about 6 million soldiers, and the Central Powers about 4 million.
However, World War One death records only provide estimates of casualty numbers, and vary according to source. The War Office official report in 1922 listed 9 million soldiers killed or missing in action, dead from wounds, or whilst prisoners of war, and included the Royal Navy war dead and missing, and the Royal Flying Corps, Royal Air Force and Royal Naval Air Service war dead, although the latter were not listed separately. These ww1 records did not include the 14,000 deaths reported by the Merchant Navy.
Despite the high numbers of military veterans recorded as deceased, and the Spanish flu pandemic which swept through the combatants in 1918, the number of soldiers died in the Great War from disease was far less than in 19th century conflicts, mainly thanks to improvements in medicine. Nevertheless, death from disease still accounted for one third of total military deaths during WWI.
887,000 soldiers from the UK and colonies died in the Great War, and more than 1.6 million were wounded, according to the Commonwealth War Graves Commission Annual Report 2009-2010, which also included Newfoundland in its ww1 military records.
In all, the total number of World War One deceased military personnel ranks fifth on Wikipedia's all time list of wars by death toll. At the top of the list is World War 2.