Did killing Cesar at the end of Fallout New Vegas teach us nothing?

The war machine is too far along to be stopped easily.

Or if WW1 is your poison:

Initially, Wilhelm II wanted to halt the German mobilization, hoping for a peaceful resolution. However, Moltke insisted it was too late to stop the complex mobilization process once it had been set in motion. He argued that it was "like a wound-up clock" that couldn't simply be unwound. His words essentially conveyed that the mobilization machinery, once started, would continue inexorably towards war, effectively removing any possibility of reversal.