1. The assassination of Archduke Franz Ferdinand of Austria-Hungary.
2. The use of toxic gases also i'd assume the over the top and into no mans land warfare.
3. For Russia, World War I was an unprecedented disaster: Russian casualties were greater than those sustained by any nation in any previous war. Meanwhile, the Russian economy was hopelessly disrupted by the costly war effort, and in March 1917 riots and strikes broke out in Petrograd over the scarcity of food.
