Started in Europe in 1919. Extremely bloody war, trench warfare, and high number of casualties in Europe (France, Germany, and Britain each had between 1-2 million dead).
Wilson issued a proclamation of neutrality, not a fair description.
Before the war, US had vastly more trade to the Allies in the war, American bankers aided the Allies, i.e. grain, ammunition
"Preparedness" - 1915 - preparing to persuade Americans that the US should enter the war
Prospect of war faced a lot of resistance, especially in the midwest - many immigrants from Germany or other Central Powers
Wilson in 1916 promised not to send the US into war, but changed his mind in 1917
Germany started to execute unrestricted submarine warfare, so Wilson asked for war, Congress declared war four days later
Huge mobilization started immediately. Entrance did help to end the war because the US was able to send a very large numbers of troops. US lost 117,000 men.
Treaty of Versailles demanded punitive reparations from Germany, also led to Wilson's 14 Points and the creation of the League of Nations.