British tanks with trench-crossing equipment, advance with troops in support, during trench warfare in France during the First World War, 1918.
Saturday marks the 100th anniversary of the assassination of Franz Ferdinand, an event that set off four years of war in Europe.
World War I also saw the introduction of new technologies that changed society. From tanks to machine guns, radio communications to air travel, blood banking to sanitary napkins, the so-called "Great War" was a bridge between the 19th century Industrial Revolution to the 20th century modern era.
Here are a few innovations – good and bad – that first saw light during a conflict that lasted from 1914 to 1918, and left 37 million soldiers and civilians killed or wounded.
An officer using a radio during World War I.
Wireless radio was first used in the war to command armies and navies, but heavy batteries required 12 men to carry portable units. On the front lines, commanders were forced to use runners, dogs, flares, carrier pigeons or even flags to relay information, or bury cables between trenches. Ships used signal lights and flags to communicate with each other because long-range radio networks were overcrowded.
Still, mass communication technology took off after the war, leading to the widespread use of radio and television.
Anna Rochester,with the American Red Cross Smith College Unit, ministers to severely wounded soldiers in France during World War I.
The First World War was the first where combat killed more men than disease, the result of improved field hygiene, clean water, disinfestation of clothing and bathing. The war also saw the first widespread use of blood banking and transfusions, which saved countless lives. Disposable sanitary napkins were first used by French nurses to stop bleeding of soldiers, later picked up by commercial firms and marketed to women.
British machine gunners firing during the Battle of the Somme.
The war saw the advent of chemical weapons, mustard gas, chlorine and phosgene that left 1.3 million soldiers horribly burned and disfigured for years afterward. Gas was used by German, French, Italian, American and British forces. Post-war treaties banned its use, but hasn’t stopped some nations from deploying them, including recently in Syria.
World War I fighter pilot Eddie Rickenbacker, known as the "ace of aces," sits in his Spad XIII fighter plane.
The first use of an airplane in war was by the Italians against the Libyans in 1911, but by 1914 the British, French and Germans had developed air forces mainly for reconnaissance. Dogfights in the air were important for morale and holding "territory," but aerial damage ground targets was limited. Advances in aviation communications, radar, avionics and safety led to a new commercial aviation industry in the 1920s.
A German submarine rises to the oceans surface in rough seas.
Armored underwater vehicles go back to the Civil War (and before), but the Allies and the Central Powers both developed submarines and German U-boats that could launch torpedoes to destroy military and civilian ships. The rules of engagement (giving merchant ships warning) were thrown out by the German u-boat fleet, and led to the sinking of the passenger ship Lusitania in 1915 with the deaths of 114 Americans among the 1,100 victims.