It was pretty much a case of everyone not being sure who to declare war on because the alliance system was so complicated that the foreign ministers barely understood it themselves and everyone was so economically tied together before 1914 that it made everything weird. Britain was importing the majorly of its glassware from Germany before ■■■■ hit the fan as just one example. And what’s kind of ironic is the majority of scopes Britain stuck on their rifles to counter snipe German snipers were German in origin. France got a ton of its steel from Germany before the war, and Germany was importing a ■■■■ ton of French alcohol products. People were genuinely surprised when they all started killing each other because of economically interdependent they all were.