U.S. Secretary of Defense Leon Panetta attended a ceremony in Baghdad that marked the official end of the war in Iraq. All troops will pull out by Dec. 31. "Let me be clear, Iraq will be tested in the days ahead—by terrorism, by those who would seek to divide" Panetta warned, as the symbolic battle flag of the U.S. was lowered Thursday. But he hailed the service of the armed services and the Iraqi people—nearly 4,500 U.S. soldiers and tens of thousands of Iraqis have lost their lives in the war that began nearly nine years ago. But Panetta said "your sacrifice has helped the Iraqi people begin a new chapter in history, free from tyranny."