World War I was started generally because of Franz Ferdinand's death, but there are some background information before this as well.
MAIN
M = Militarism (Everyone wants to show off their strength, why not do it with military power? Many nations kept building up their armed forces to show the other what "true power" looks like, leading to a sort of "arms race" except it wasn't exactly a race, more like a contest)
A = Alliances (Triple Entente and the Triple Alliance; 6 powerful nations gathered into teams and promised to assist each other if war broke out causing a chain reaction)
I = Imperialism (People like to be in control of things, therefore they crave power, they want to take control of others and add the nation's power to theirs)
N = Nationalism (Every nation wants their nation to be the best therefore they supposed economic and territorial gains, such as imperialism)
