At the beginning of the 20th Century, economic, colonial and national rivalry led To increased tension between European states. An arms race began that Eventually led to the outbreak of the First World War (1914-1918).
This was a new type of conflict that involved many different countries. It Mobilised not only armies but also civilians, and brought widespread death and Destruction.
The Russian Empire's participation in the war led to a two-phase revolution in 1917 that brought tsarist autocracy to an end and established the world's first Socialist state.