Moreover, as China's trade and aid to North Korea have continued to grow, U.S.-led sanctions have not had their anticipated effect of undermining the North Korean regime. To the contrary, there are signs that Washington's ability to influence North Korea's behavior, including its nuclear program, is on the wane.

According to Katharina Zellweger, the former head of the Swiss Agency for Development and Cooperation who worked in North Korea for 15 years, there are rumors that China already has or is planning to send food aid and fuel, though the amount is unclear.

"Why would [North Korea] deal with the United States?" she said. "The train has left the station."

This week's diplomatic breakthrough may indeed be one of the last opportunities Washington has to influence Pyongyang's nuclear program. As Secretary of State Hillary Clinton put it at a Senate hearing, "The world is transforming around us."