An example would be World War I, if the allies of Austria-Hungary and Serbia were not involved, it wouldn’t have ended up into the First World War. Alliances were formed for safety, power, military weapons and soldiers to insure a country’s safety. Now it’s a matter of who is stronger or better. A single event in one country would variably involve the other countries. A tug on one string tugged the rest, and thus the whole continent fell into war.
06 May 2014. "Weapons of War." First World War.com. N.p., n.d. Web.