Douglas Haig — British Soldier born on June 19, 1861, died on January 28, 1928

Field Marshal Douglas Haig, 1st Earl Haig, KT, GCB, OM, GCVO, KCIE, ADC was a British senior officer during the First World War. He commanded the British Expeditionary Force from 1915 to the end of the war. He was commander during the Battle of the Somme, the battle with one of the highest casualties in British military history, the Third Battle of Ypres and the Hundred Days Offensive, which led to the armistice in 1918... (wikipedia)

Obviously, the greater the length of a war the higher is likely to be the number of casualties in it on either side.
The idea that a war can be won by standing on the defensive and waiting for the enemy to attack is a dangerous fallacy, which owes its inception to the desire to evade the price of victory.
Further, a defensive policy involves the loss of the initiative, with all the consequent disadvantages to the defender.
So long as the opposing forces are at the outset approximately equal in numbers and moral and there are no flanks to turn, a long struggle for supremacy is inevitable.
Once the mass of the defending infantry become possessed of low moral, the battle is as good as lost.