WWI broke out on July 28, 1914, and endured for four long years until a truce was finally declared on November 11, 1918—a date that would later become an annual commemorative event known as Armistice Day, or Remembrance Day. The war was fought between two sets of allies: the Triple Entente (France, Russia, and Britain) and the Triple Alliance (Germany, Italy, and the Austro-Hungarian Empire), all of which were major European powers with vast territories and resources at their disposal.

While there had of course been countless armed conflicts before throughout history, this conflict became known as the First World War due to its truly global scale and its staggering death count: Estimates of the total military and civilian death count often exceed 10 million, with tens of millions more injured, missing in action, or otherwise affected by the conflict. The war also saw major developments in military technology, such as the use of chemical weapons—especially the infamous mustard gas, which blinded and suffocated soldiers caught without a gas mask—and aerial bombardment. The war is also famous for its trench warfare, in which opposing forces spent much of their time living and fighting from a long series of deep ditches (or trenches) that usually left the soldiers exposed to the elements and living in deeply unhygienic conditions that exacerbated deadly communicable diseases.