In which year did the First World War start?

The First World War started in 1914, which is widely recognized as the beginning of one of the most significant conflicts of the 20th century. This year marks the outbreak of the war following the assassination of Archduke Franz Ferdinand of Austria-Hungary, which set off a chain reaction among the major European powers due to existing alliances and tensions. The conflict lasted until 1918, fundamentally altering the political landscape of Europe and leading to significant social and economic changes worldwide.

Other years mentioned, like 1900, 1910, and 1920, do not correspond to the start of the war. While the early 1900s were characterized by increasing militarization and political tension, it wasn't until 1914 that the formal hostilities began. The year 1920 marks the aftermath of the war and the signing of important treaties, not the start of the conflict itself.