Possible Clues:

• The US joined it in '17
• Doughboy's conflict, briefly
• Sgt. York served in it
• Historical event given its current name in 1939: Abbr
• 'Sucker Punch' setting, briefly
• Setting of the Robert Graves memoir "Good-bye to All That," in brief
• "All Quiet on the Western Front" subj
• Chapter in early 20th-century history: Abbr
• Its end is commemorated on Nov. 11
• Armistice Day conflict