Which statement best describes the reason that the Allied war effort was so successful

The correct answer is 2.

The role of women in the American economy during World War II was critical. Considering that millions of American men were drafted into the US army during this time, this left open a significant amount of factory jobs. These jobs building guns, ammunition, airplanes, etc. were often taken by women. Women redefined their role in American society and proved that a woman can do a "man's job" in terms of working in industry. Women were encouraged to join the workforce through propaganda like Rosie the Riveter.

The second one seems the most reasonable