The World Cup that kicked off this week in Australia and New Zealand is a time to rejoice in the dominance of American women in international sports.

It also occurs at a time when the conversation about women in sports is turning on its head in the US. After decades spent making sure women have access and support to play sports, there's now a politically loaded debate over who is considered a woman -- a motivating issue for Republicans over the last year.

The US has invested in giving women access to sports like no other country, building for decades on the Title IX law that required equal opportunity.

If the US women lose the FIFA World Cup tournament, it will be a sign that the rest of the world is catching up. But there's a good chance the American system will have had a direct role in helping the victor.

Twenty-one of the 32 teams taking part in the tournament have at least one woman who played college soccer in the US, according to the NCAA.

Still a long way from equality for women

While American women achieved a historic agreement last year with the US Soccer Federation to earn wages for their international duty on par with the middling US Men's National Team, most female athletes still make a fraction of what their male counterparts bring in.

A CNN analysis published Thursday finds that female soccer players earn 25 cents to the dollar of men at the World Cup. And according to a report from the global players' union, two-thirds of surveyed women competing in World Cup qualifying rounds had to take unpaid leave from another job to compete.

That's all assuming there is a team in a woman's country. In Saudi Arabia -- which has its sights on taking over multiple professional men's sports by throwing money at golf and soccer -- women only played their first international soccer match last year.

But there is a growing political debate in the US not on continuing to level the playing field for women, but on reacting to the fraction of athletes assigned male gender at birth who are trying to compete as women.

The swimmer Lia Thomas created controversy when she changed from the men's to the women's team at the University of Pennsylvania and won an NCAA title in the 500-yard freestyle last year.

The international governing bodies of swimming and track and field have since banned transgender athletes who transition from male to female after going through puberty from competing at the international level, which means Thomas will not be eligible to compete in the Olympics.

Multiple US states have likewise passed laws that ban transgender women and girls from participating in sports teams that align with their gender identity. However one feels about whether a person who went through puberty as a male should compete with biological women, the fact that these laws prohibiting trans athletes are paired, as they were in Missouri last month, with efforts to ban gender-affirming care for minors would seem to create a catch-22.

FIFA, the governing body for world soccer, has been in the midst of a review of its policy on gender for the past year and for now defers to countries to verify that competitors are either women or men, which has created some awkward situations in recent years, as Reuters reported. The NCAA will defer to the rules of the governing bodies for sports.

In April, the US House passed the "Protection of Women and Girls in Sports Act," a GOP-led bill that would update Title IX to ban transgender athletes from women's and girls' sports at federally funded schools and educational institutions.

There is some irony in the fact that Republicans want to update a law that was designed to make sure everyone could play sports in order to exclude people who don't fall easily into gender categories.

Why Title IX exists

Title IX was passed in 1972 at a time when women trying to compete in sports were treated with hostility. In 1967, for instance, the runner Kathrine Switzer had to sneak onto the Boston Marathon course and evade race officials to complete the marathon.

This year, there was a nonbinary division for the race, a rare accommodation at a time when there is so much attention being paid to who should be allowed to compete in women's sports.

The Canadian soccer player Quinn, who uses "they" and "them" pronouns, is a nonbinary athlete who will play at the Women's World Cup. They made history as the first trans person to win an Olympic gold medal at the Tokyo 2020 Olympic Games, which were played in 2021. They played college soccer for the women's team at Duke University.

The US soccer star Megan Rapinoe, an outspoken defender of LGBTQ rights who is competing in her final World Cup, was critical of the current political efforts regarding transgender athletes.

"We as a country are trying to legislate away people's full humanity," she told Time magazine in an interview, according to CNN's report.

"It's particularly frustrating when women's sports is weaponized. Oh, now we care about fairness? Now we care about women's sports? That's total bullsh*t. And show me all the trans people who are nefariously taking advantage of being trans in sports. It's just not happening," she said.

Last year, CNN published a succinct and informative look at how Title IX has changed not just the US sporting landscape, but the entire country. Watch it.

"I think it's important to realize that for every step forward that Title IX has made in terms of safeguarding gender equality, there has been pushback and there has been backlash," says Natalia Mehlman Petrzela, a history professor at The New School.

I reached out to Petrzela to ask how the gender debate has evolved over the past year.

"People are really looking at women's sports again, through a critical lens and thinking about what equality and equity means that both recognizes the difference of women but that also that reevaluates the category of woman," she said.

While there is zero chance Republicans' anti-transgender athlete bill becomes law with Democrats in charge of the Senate and the White House, the Biden administration demonstrated the difficulty of this issue when it opposed blanket bans on transgender athletes while allowing for some restrictions.

"The proposed rule also recognizes that in some instances, particularly in competitive high school and college athletic environments, some schools may adopt policies that limit transgender students' participation," according to the administration's proposal for a federal rule.

It's clear that no one knows the right answer to this question at the moment, as gender definitions evolve.

"I'm really skeptical of people that have total certainty on this issue right now," said Petrzela. "I think it's really complicated."

But she raised a key issue that we can foresee: what happens if schools or leagues want to verify an athlete's gender?

"What I worry about a lot is that this increased scrutiny on who's a real girl is going to give a license to all kinds of authorities and institutions to be inspecting and policing girls' bodies," she said.

To that point, the Florida High School Athletic Association was pressured earlier this year to remove questions about menstruation from a required medical evaluation form.

Most states currently require or request information about menstrual cycles from high school athletes, according to CNN's report.

But these questions will come under new scrutiny as laws against transgender athletes take effect.

And this debate will continue to evolve.