From Military Times:

“The American departure represents a joyous event, but our concerns are about the time after the departure,” the Tikrit schoolteacher said. “Absolutely, after the American withdrawal the divisions between Sunnis and Shiites will get worse and worse.”

Toward the end of the occupation, many Sunnis came to feel that the American military was treating them fairly, or at least was more fair than the Shiite-led government. They fear that the U.S. departure means the loss of a protector.