World War I (1914-1918) was a war involving over a hundred nations that arose from existing tensions in Europe that manifested themselves through a network of alliances. The casus belli of the war was the assassination of Archduke Franz Ferninand, the heir to the Austro-Hungarian empire, at the hands of Serbian Gavrilo Princip. Princip, like the nationalists he represented, wanted to eliminate Austro-Hungarian sovereignty over Bosnia. In 1873, long before the assassination of the Archduke, the German chancellor, Otto von Bismarck acted on his concern over the power of England and France by signing a mutual defense agreement with Russia and Austria. Russia and Austria, however, had their own conflict over control of the Balkans, and so Russia exited the agreement, leaving the double alliance of Austria and Germany. This was soon joined by Italy, and eventually, others. Those who would oppose them in the war were Russia, the British empire, France, and myriad other countries, including the United States.
World War I was characterized by its high number of casualties –estimates range from between fifteen and twenty two million deaths– and its pioneering of modern technology. The war was often a defensive one fought in trenches as soldiers battled machine guns, new use of chemical warfare, flame throwers, and the disease rampant within the trenches.
1.5 Million Indian men were summoned to fight for England, their colonizer. More than half a million of these men worked as laborers who built infrastructure and carried supplies. The rest held combatant roles. Haimabati Sen’s second son, Atmajyoti Sen, fought in the war as a captain in Mesopotamia and joined the Indian Medical Service. He survived the war, and lived until 1970.
Sources
Because I am a Woman by Haimabati Sen, photographs and captions between chapters 12 and 13.
https://www.britannica.com/event/World-War-I
https://www.history.com/topics/world-war-i/world-war-i-history