Answer:
The First World War began in 1914 and ended in 1918. This was the first time chemical weapons had been used and the first bombs dropped from aircraft. The two main sides were the Central Powers (the German Empire, Austria-Hungary, the Ottoman Empire and the Bulgarian Empire) on the one hand and the Allies (or Entente Powers) on the other: France, British Empire, Empire Russia, the Kingdom of Serbia, Montenegro, Japan, Italy, Portugal, Romania, United States of America, Greece and Siam. This was the first modern war to rely on weapons technology and spread terror between ordinary non-soldiers.
It ended with the signing of the Compiegne armistice on November 11, 1918, which established the defeat of the Central Powers. Throughout the war, both sides had to adapt to new strategic situations that they were not prepared for. They responded with an unprecedented military escalation in European history that resulted in a total of nine million deaths.