The answer would be, The role of women in world war 1.
Short explanation : Most of the men were at war and and the woman had to start working/get jobs. Women typically around WW1 were seen as housekeepers, and only house keepers, and society did not believe that they could hold steady jobs.
...Its the reason why you have your freedom? The reason we aren't under the control of the British Empire? Why didn't you learn this in second grade? It was the reason America is well... America. It was the first war America fought for the freedom of her people. One could argue the most important war in American history, and possible even the WORLD for that matter, because who knows what the world would be like today if America didn't come to be.