Traditions break down fast during times of war, and history is full of examples where women assumed dramatic new roles that never would have been possible in times of peace.
As this photo gallery shows, the pressing demands of World War II led many countries to call on women to bolster their armed forces, in jobs ranging from nurse to front-line soldier.
Hundreds of thousands of American women served in the U.S. military during that war, and U.S. women were allowed to fly military aircraft for the first time. Some countries desperate for fighters, like the Soviet Union, put women in combat roles.
When wars end, old rules can often return. The U.S. Congress mandated in 1948 that women should be limited to 2 percent of the force. Women have managed to steadily expand their role in the military since then, and they now make up 15 percent of the military.
But they were barred from combat positions until Defense Secretary Leon Panetta announced Thursday that he was ending that policy.
The U.S. has plenty of examples to learn from. Many European countries, along with Canada and Israel, have permitted women in combat roles for years, citing gender equality. Some Communist countries have also turned to female soldiers for reasons of ideology or propaganda.