As the United States turns 250, we asked foreign policy experts about the moments in American history that changed the world.Middle East expert @stevenacook says the 9/11 attacks were one of the most consequential moments in U.S. history. While the aftermath was a moment of unity for the country, he argues that the response to the attacks distorted domestic politics and contributed to the destabilization of the Middle East. "These are prices that we are continuing to pay, 25 years later."