I think GP did mean WWI, where one event [1] set off a chain reaction of mutual defense assurances until first all European powers, then all major world powers

I think GP did mean WWI, where one event [1] set off a chain reaction of mutual defense assurances until first all European powers, then all major world powers were at war. [1] https://en.m.wikipedia.org/wiki/Assassination_of_Archduke_Franz_Ferdinand https://en.m.wikipedia.org/wiki/Assassination_of_Archduke_Fr...