They had allies who were at war with each other, so they had to go to war in support of their allies.
Britain needed a “Brexit” in 1914.
> They had allies who were at war with each other, so they had to go to war in support of their allies. <
That’s true (WW I). And there is perhaps a lesson in that. Must a nation support its allies regardless of the risk?
Consider the small Baltic nation of Latvia. Latvia borders on Russia. And Latvia is far - very far - from the United States. And Latvia is of no strategic interest to the United States.
Yet Latvia is a member of NATO. So the US is allied with Latvia. If Russia should ever invade Latvia, must the US respond? Should the US risk it all - nuclear war - to defend Latvia?
I actually don’t know about that. But it’s the same question the UK and France faced in 1914. Is it worth it for the UK and France risk everything because of Serbia? (Recall that WW I started because a Serbian nationalist shot an Austrian duke.)