The number of women in prison worldwide has risen by nearly 60 percent in the past two decades, according to the Institute for Crime & Justice Policy Research (ICPR).

That rate is almost three times the rate of the male prison population increase. But women's rights summits, such as the UN-backed Women Deliver Conference, have been criticized for excluding the subject from the spotlight.

Many women in prison have histories of poverty, mental illness, or are victims of physical or sexual assault. Additionally, most of them are mothers, and there are at least 19,000 children living in prison with a parent, according to the United Nations.

Poverty, structural inequality, and the war on drugs are key factors contributing to the rise of female imprisonment. Additionally, increased rates of incarceration have been seen in both developed and developing countries across the globe.

In the United States, over 200,000 women are in prison — more than any other country, according to the ICPR. The U.S. also has the highest female prison population rate of any nation, at a staggering 64 women per 100,000 of the general population. Other comparable nations included Thailand, El Salvador, Turkmenistan, and Brunei Darussalam.

In an open letter, hundreds of incarcerated women and activists have demanded that they are no longer excluded from women's rights forums. The letter, coordinated by Women Beyond Walls (WBW) and signed by 115 organizations, denounced the Women Deliver Conference for excluding women's incarceration from their priority list.

"This is reflective of the marginalization of the realities of incarcerated and formerly incarcerated women across high-level forums," they said, adding that it "contributes to lack of funding and policy reform which is needed to address the alarming increase in the criminalization of women."

Over two-thirds of organizations surveyed worldwide by Women Beyond Walls reported that they do not receive funding from women's rights foundations.

"I think it’s overlooked because we like to support women if they fit into the stereotype of what is ‘marketable’," Lawyer and WBW founder Sabrina Mahtani said, via The Guardian. "These are some of the most marginalized women and, really, we shouldn’t be looking at numbers; we should be looking at who are the women who most need support and help."