World War I: In the culmination of the July Crisis, Austria-Hungary declares war on the Kingdom of Serbia and begins the Great War.

World War I, or the First World War, also known as the Great War, was a global conflict between two coalitions: the Allies and the Central Powers. Major theatres of war included Europe and the Middle East, and well as parts of Africa and the Asia-Pacific. One of the deadliest conflicts in history, World War I resulted in an estimated 15 to 22 million deaths, including in mass war crimes against civilians and genocides.

The conflict saw important developments in weaponry, including the first large-scale use of machine guns, artillery, aircraft, chemical weapons, and tanks, and was a major factor in the deadly Spanish flu pandemic.

Bataille de Verdun 1916
Bataille de Verdun 1916 (Source: Wikimedia Commons)
British 39th Siege Battery RGA Somme 1916
British 39th Siege Battery RGA Somme 1916 (Source: Wikimedia Commons)
American troops going forward to the battle line in the Forest of Argonne. France, September 26, 1918. - NARA - 530748
American troops going forward to the battle line in the Forest of Argonne. France, September 26, 1918. - NARA - 530748 (Source: Wikimedia Commons)
Germanmachineguncrew1918
Germanmachineguncrew1918 (Source: Wikimedia Commons)

Watch: World War 1- A BBC Documentary

From the Documentary Time channel.

Sources and further reading: Wikipedia — World War I, July Crisis, Austria-Hungary, To my peoples (CC BY-SA). Images: Wikimedia Commons.