Lets look at the facts as we know them.
WW1

Germany declares war on Russia and France August 1, 1914
August 1914 Bulgaria and Turkey join Germany and Austria-Hungary
in the Central Powers. France, England, Russia (later Japan and Italy) join the Allied Powers

Wilson declares U.S. neutrality August 4, 1914
Wilson calls for "peace without victory" January 22, 1917

Zimmermann note discovered February 1917 Berlin to Mexico City
Foreign minister Zimmermann asks Mexico to join Germany in exchange for return of southwest U.S. British intercept message

Selective Service Act passed May 28, 1917 Washington, D.C. Nearly 10 million men are listed and a lottery chooses first 687,000 to serve.
Eventually 3,000,000 men serve as draftees in the war

Cantigny May 28, 1918 North of Paris First victory for American troops
Chateau-Thierry May 1918 France French and American troops block German advance
Belleau Wood June 1918 France American forces suffer heavy losses but defeat Germans
Second Battle of the Marne July 1918 France Allied forces defeat Germans who begin retreat east
Sedan October 1918 Eastern France American troops cut German supply lines 50 miles behind German front

Germans surrender, expecting a peace drawn up under Wilson's generous 14 Points November 11, 1918 Compiegne, France
Worst war in world history is over. 10 million soldiers killed, 10 million civilians die from disease and starvation

(It took America 6 months to defeat the Germans the first time) After trying to avoid the war and while negotiating for peace for 2.5 years
to no avial.