The United States' role in world affairs was very limited
Some became soldiers through out the war
The first option is the best source. it is written by an authority on the topic.
The Assasination of Archduke Franz Ferdinand.
Also Militarism was one of the reasons.
Remember this----> M-A-I-N= Militarism Alliances Imperilism Nationalism
those are some causes of WW2
George Washington the 1st president.