Where is 'red line' on rape in war?

I remember a chalk line drawn on blacktop by a group of kids at recess when I was young. The message was clear: This is the line you do not cross. If you stepped over it, you would face the wrath of those kids in whatever game we were playing. Now turn that line crimson and color it toxic. This is the adult version of "do not cross."

This is the infamous red line.

We first heard about it in terms of Syria a year ago. President Barack Obama said that the use of chemical weapons by Syrian President Bashar Al-Assad would cross a "red line" that would have "enormous consequences." As chemical weapons were deployed in Syria in August, Obama's tripwire was triggered. Then Obama told reporters: "First of all, I didn't set a red line. The world set a red line."

When Obama says "the world" did it, he was indicating that much of the world long ago decided chemical weapons were an abhorrent thing to unleash in war. More than 160 countries signed a treaty attesting to this view.

But why has "the world set" this one line in the blacktop, and not others? The United States and its allies ignore the violation of treaties all the time. They ignore the use of other terrible weapons in global conflicts daily. As someone who grew up wondering why we intervened in Bosnia but not Rwanda, as someone who directs a project on rape in war, I want to know: How do we decide what suffering matters enough to get a red line?

At the Women's Media Center's Women Under Siege project, we've been keeping a live crowdmap of sexualized violence in Syria. I've personally reported multiple stories of rape in which women were hung by their wrists or burned. We've also documented how hundreds of thousands of women have been raped in 16 years of fighting in the Democratic Republic of Congo.

Yet Congress is not debating whether to intervene in Congo. It is not struggling over what to do about the rape and torture of women and men in Syria or anywhere else. Why? Here's one gut-wrenching answer:

"People divide their understanding of militarized violence into normal and not normal, acceptable and not acceptable," says Yifat Susskind, executive director of women's human rights organization MADRE.

To read the rest of this op-ed, please click over to CNN.com.