The u.S. declared war on Germany on 6 April, 1917.  The American Expeditionary Force (AEF), under the Command of Gen. John J. Pershing, was formed on 5 July 1917.
The American Battles in World War I were fought during 13 campaigns.  The most famous were:
The Battle of Cantigny fought on May 28, 1918.

The Battle of Chateau-Thiery fought between 3 June 1918 and 26 June 1918

The Battle of Belleau Wood fought on 6 June 1918 - 26 June 1918

The Battle of St. Mihiel fought on 12 September 1918

The Battle of Argonne Forest fought between 26 September and 11 November 1918
Fighting ceased on the 11th hour of the 11th day of the 11th month after the armistice went into effect,  The last battle of WWI.  The date is celebrated as Armistice Day in many countries, Remembrance Day is some and Independence Day in Poland.   In the U.S. it was changed to Veterans Day on May 13, 1938.