Aid workers fear a new disaster as militia forces close in on a major Darfur city.

On a sunny April afternoon in 2006, thousands of people flocked to the National Mall in Washington, D.C., for a rally with celebrities, Olympic athletes, and rising political stars. Their cause: garner international support to halt a genocide in Sudan’s Darfur region.

“If we care, the world will care. If we act, then the world will follow,” Barack Obama, then the junior Illinois senator, told the crowd, speaking alongside future House Speaker Nancy Pelosi. That same week, then-Sen. Joe Biden introduced a bill in Congress calling on NATO to intervene to halt the genocide in Sudan. “We need to take action on both a military and diplomatic front to end the conflict,” he said.