Question

How did the formation of alliances affect the outbreak of war?

Answer 1

If you're talking WW1, alliances pretty much set it off as everyone was suddenly obligated to go to war. In short, it went like this:

Austria-Hungary gave Serbia an ultimatum they knew they couldn't accept. When they didn't, Austria-Hungary declared war. Serbia, however, was friendly with Russia, so Russia mobilized. Germany responded with a mobilization of its own and told Russia to back off. When Russia refused, Germany declared war on Russia. Germany's war plan also called for a swift knock-out of France before turning against Russia later, so they declared war on France as well. Shortly after that, Britain declared war on Germany. And like that, Europe was set on fire.

Crazy, eh?