The event that is considered a MAJOR turning point in favor of the Allies in World War I is:
D - Zimmerman Note and entrance of the U.S.
The interception and publication of the Zimmerman Note in early 1917, in which Germany encouraged Mexico to join the war against the U.S., along with the subsequent entry of the United States into the war, significantly bolstered the Allies' resources and morale, ultimately contributing to their victory.