The war had started when a Serbian nationalist had shot Archduke Franz Ferdinand of the Austro-Hungarian Empire.
The deadliest fight of the war was the 100 Day Offensive, where for 100 days, the Allied armies charged over the trenches and attack the Central trenches, at the end of it, both sides lost over one million soldiers.
Many modern weapons were not only invented but mas producded, and the research for these weapons were also accelerated. For example, better radio communication, better mortars, cannons, aircraft, tanks and much more.
Trench warfare was incredibly brutal. Millions of men along hundreds of miles of trenches, not only being compact but also smelly. The trenches also filled up with water very easily, causing foot corrosion known as trench foot. Constant artillery bombardment killed many people, as well as rats and lice which also plauged the trenches.
The war ended on November 11th, 1918, when Germany had formally surrendered, then the treaty of Versailles started, and the treaty negoations ended on June 28, 1919
The effects of the World War one were felt across the world, millions were dead, Russia was in chaos, Austria-Hungary was disbanded into many smaller countries, Poland was reborn, partially splitting Germany, the Ottoman Empire was turned into Turkey, and Germany had to pay 800 million dollars that it didn't have which caused economic ruin and uproars for change.