But the United States is not a global trailblazer when it comes to putting women on the front lines.
From the female "Battalions of Death" in Russia to the ancient "Amazons of Dahomey" of modern-day Benin, women have historically protected their nations against the threat of enemy force. Today they participate in many military conflicts around the world. For example, women in Israel, who have served in the Israeli Defense Forces since the country's founding, have been able to participate in combat for nearly 15 years.
But even if the US is not ahead of the curve in allowing women to serve in the most dangerous roles, the move, announced by US Secretary of Defense Leon Panetta Jan. 24, could reverberate worldwide.
Women have historically served in combat positions when a demographic need requires it. Soviet armies, for example, were filled by women during World War II. The US move is also in part an acknowledgment of the roles women have played in the wars in Iraq and Afghanistan, as demand for soldiers has swelled over the past decade.
But it's not just about numbers. It's also about equality.
"The department's goal in rescinding the rule is to ensure that the mission is met with the best-qualified and most-capable people, regardless of gender," Mr. Panetta said.
The US joins a number of countries, from Canada to Australia, that are pushing against old notions that women have neither the stamina nor strength to serve on front lines, that they should be home mothering children, or that militaries are better off without sexual tension in the barracks. That could have implications for armies around the world, from countries in Europe to Latin America to Africa, where women are still confined to gender-specific tasks.
"[The US is] not the first, but they are in the vanguard," says Nancy Duff Campbell, copresident of the National Women's Law Center, who has pushed for women's rights in the military. "I assume we'll be able to do it well and effectively and become a model for the rest of the world."
Women's presence is limited
Countries around the globe have opened militaries to women, but even in countries where women have the right to be in combat roles, their presence is limited. Among the world's most famous female soldiers are Israelis: In 1948, upon the founding of the state, Israel became the first country to draft women as part of its mandatory military conscription. They've been in combat roles since 2000, following a landmark ruling by the Israeli Supreme Court. Over the past dec-ade, the number of positions open to women in the military has reached 90 percent (though some combat roles in the special forces, the artillery corps, and infantry divisions remain closed).
The number of female career officers in Israel has increased by 40 percent since 2000, according to military statistics. In 2011 Orna Barbivai became the country's first female major general.
Still, the presence of women in combat remains relatively rare, even in Israel: In 2011 only 3 percent of combat officers were women. Yoav Gelber, a professor of Israeli military history at Haifa University, says that many Israelis still see female combat as a rarity. "It's an exception ... most people think women can fulfill so many roles in the army besides combat," Mr. Gelber says.
It is not only in conflict zones that women are a growing fixture in combat positions. In 2009 in China, the People's Liberation Army Air Force graduated its first class of female fighter pilots, and a year later the Chinese Army founded its first all-female missile-launching unit. In 1993, Japan opened nearly all combat positions to women, who now make up 5 percent of the Japan Self-Defense Force. But, unless Japan is directly attacked, its troops should never be involved in combat.
In Pakistan, going off to fight for one's country was always considered a "man's job," with women only allowed to serve in military hospitals. But in 2006, Pakistan's military saw its first recruitment of female officers as combat pilots and in noncombatant positions. When the first female pilots were inducted into the Air Force, then-Vice Chief of Army Staff Gen. Ahsan Saleem Hyat said they had "shown the spirit and courage to rise above the ordinary and break new ground for others to emulate."
Analyst Ejaz Haider, who covers Pakistan's Army, says the reaction to women joining combat forces was positive. "People ... felt a sense of pride in belonging to an organization that is giving an equal opportunity," Mr. Haider says. "There wasn't anything close ... to the debate in the US about gays serving in the military."
Five European countries allow women to serve in combat divisions: Denmark, France, Germany, the Netherlands, and Norway, according to a British Ministry of Defence study, which reports that Nordic countries have been some of the more-progressive nations in Europe, taking on total-inclusion policies that aim to be gender neutral.
Norway allowed women in combat forces in the mid-1980s, and later became the first NATO country to allow women in all combat functions, including submarines, according to the British Ministry of Defence. But Norway's strategic goal of getting a 15 percent female representation in the military has still not been met, according to the Norwegian Ministry of Defence.
According to European Union equality laws, member countries must revisit the issue of women in combat roles every eight years. When Britain last addressed the issue in 2010 it maintained the exclusion of women from combat, with then-Minister of Defence Andrew Robathan citing threats to troop "cohesion" in intense battle situations.
On paper, European armies look good in terms of gender equality, but in reality it doesn't always play out that way.
"In many European countries, there are more restrictions on the duties women can perform in the armed forces than in the US. As a result, women play less of a prominent role," says Clara O'Donnell, a senior fellow at the Centre for European Reform in London.
Part of this state of affairs might be tied to the reliance, until recently, of a number of European countries on conscription. In addition, militaries tend to be smaller in Europe. This can make it harder, or comparatively more expensive, to create quarters that can accommodate both genders, Ms. O'Donnell says.
NATO sometimes requires its partners, such as the Afghan government, to introduce higher benchmarks for female participation in their armed forces than those observed by NATO allies themselves, O'Donnell says.
In Latin America, women are sidelined
Although Latin American women played a role in rebel movements like the Sandinistas in Nicaragua, today, in modern armies, they are sidelined. Adam Isacson, a security policy expert at the Washington Office on Latin America, describes militaries in the region as classic "old boys networks," and notes that women's rights movements in Latin America lag behind those in the US. "A lot of the focus has been on getting women more involved in politics, or rights to abortion, but certainly no strong demands on participation in the armed forces."
But militaries have increasingly been opened to women over the past decade. In Mexico, women have joined ranks amid personnel shortages, says Dr. Roderic Camp, a Mexico specialist at Claremont McKenna College in California. The number of women in noncombat roles has significantly increased since 2000; and in 2008, the Army passed an internal regulation that allows women to obtain the highest positions in the organization. Today, 4 to 5 percent of the Mexican Army is made up of women; and in the Navy, female representation is closer to 15 percent, according to government statistics. That's about the same percentage of US women in the military.
Elsewhere in the region, Michelle Bachelet, Chile's former president and current director of UN Women, was the minister of defense prior to taking on the presidency. She helped pioneer a number of policies including making women's inclusion in the military a national policy. Women were first allowed to enroll in military colleges in Chile in the 1970s, though they were limited to administrative and teaching roles. By 2002 they could join the Air Force, and two years later, the Navy, according to a 2004 Canadian Foundation for the Americas report. In 2004 1 in 5 new Chilean officers in training was female; by 2005 women in Chile, a leader in the region, represented 15 percent of the armed forces.
And last year a Colombian senator proposed that women be included in required military service, in an effort to encourage further gender equality. The armed services "should have the support and backing of women, [and both genders] should work side by side," Sen. Juan Manuel Galán told Colombian newspaper El Espectador.
Demand has typically driven opportunity
Most countries have relied on women only when they've most been needed. During World War II, Soviet women were enlisted en masse; about 800,000 of them served in the Red Army, mostly in support and auxiliary roles. But significant numbers also fought the oncoming Nazis, as machine-gunners, tank crew members, and guerrillas in occupied territory. The Soviet Army discovered that women made excellent snipers, and employed hundreds of them on the front lines throughout the war.
Most famously, the USSR created three regiments of female aviators who went on to fly a combined 30,000 combat missions during the war. They included an entire regiment of female fighter pilots, known as "Stalin's Falcons," which shot down 38 Nazi planes in air combat, and produced two fighter aces.
But today there is a strict rule against Russian women serving in any direct combat role. "The Russian armed forces are rather old-fashioned about this," says Alexander Golts, a military columnist for the online newspaper Yezhednevny Zhurnal. "Women serve as signals and communications technicians, medical personnel, clerks, and other support roles, but never in combat ones," Mr. Golts says.
In Africa, forced to step back from front lines
Princesses in 17th-century Nigeria commanded armies that seized dozens of cities, extending kingdoms. In Ghana, Yaa Asantewaa, a woman, led a rebellion against British colonialism known as the War of the Golden Stool.
Today, however, Africa's women have mostly been forced to step back from the front lines and are most likely to be seen in support roles that mirror their traditional positions in domestic settings. They serve as cleaners, cooks, and secretaries for armies. In no major recent conflict across the continent have women been deployed in combat positions on the order of a government, aside from during the Ethiopian-Eritrean war, when both sides sent women to the front lines. Eritrea continues to recruit female soldiers, as does South Africa, which implemented a controversial gender equality policy that aims to bring more women into the military. South African women can also serve as fighter pilots.
Africa's tradition of women warriors came to an end during and after colonization, says Helmoed Heitman, a South Africa military analyst for Jane's Defence Weekly.
"Most African armed forces took the lead from their respective colonial powers when they came to independence, and those had no tradition of women in the forces," Mr. Heitman says.
Some of this is changing. Years after initiating active female service in World War II, the Russian military, for example, spent the past decade actively courting female recruits because of a demographic crisis that sharply limited its available pool of male conscripts.
In 2009, then-President Dmitry Medvedev authorized an experiment to admit women into military academies for full training in most officer categories. One well-publicized case was the inclusion of 20 female cadets in Russia's top airborne warfare school in Ryazan, which turns out elite paratroopers.
However, Golts, the military columnist, says when the women graduate, they are likely to be left on the ground to carry out support roles. "A female paratroop platoon is something new for Russia," Golts says. "We'll see where this leads."
In other countries, including the US, some believe opening up combat roles to women is part of a slow but long-lasting change.
Canada's policy of including women in combat was the result of a 1989 ruling by its human rights court. The court stipulated that women were to be fully integrated into the Canadian Forces (CF), with the exception of submarine service, a limitation that was lifted in 2001.
The court said the CF could not justify the exclusion of women on the basis of operational effectiveness, and the CF was given 10 years to develop a plan that "steadily, regularly, and consistently" worked toward the full integration of women in combat positions.
Part of that included implementing science-based standards. For example, says Ms. Campbell, investigators found that while it was hard for women to carry wounded soldiers off fields over their shoulders, it was hard for men, too. In fact, most were dragging soldiers – something that women and men can do equally.
Australia, which announced it would open up front-line combat roles to women in 2011, also committed to a multiyear process of incorporating women into combat with scientific standards. "[In the US] this is going to be a three-year process, too. The fact that Australia did something very similar means it's very doable," says Campbell.
In some ways the US announcement just codifies what has already been practiced for years: Women were on the front lines in Afghanistan and Iraq in an unofficial capacity.
"In reality, women have been in combat all along," says Rosemarie Skaine, author of "Women in Combat." And she says that by legalizing it, the US can set an example for the rest of the world. "I think the US is looked upon as a military supreme," Ms. Skaine says. "If it works, then [other countries] might think it would work for them, too."
• Chelsea Sheasley, Fred Weir, Saba Imtiaz, Gavin Blair, Mike Pflanz, Peter Ford, and Valeria Criscione contributed reporting.