On the morning of Sept. 11, 2001, 19 members of the international terrorist organization al-Qaeda hijacked four U.S. airliners.
At 8:46 a.m., hijackers steered one plane into the North Tower of the World Trade Center in New York City. Seventeen minutes later, at 9:03 a.m., a second plane hit the center's South Tower.
A third plane carrying 53 passengers flew into the Pentagon at 9:37 a.m., and a fourth crashed into a Shanksville, Pa., field after passengers rebelled against the terrorists.
In all, about 3,000 people died, including the 19 hijackers and 246 people onboard the commandeered planes.
The nation mourned, and continues to remember the victims.
In response to the attacks, then-President George W. Bush authorized Operation Enduring Freedom, a military strike against al-Qaeda and the ruling Taliban regime in Afghanistan. The initial airstrikes targeted the cities of Jalalabad, Kandahar and Kabul, the Afghan capital.
More than 14,449 coalition and Afghanistan soldiers have died in the war, including 1,987 U.S. troops. An estimated 12,500 to 14,700 Afghan civilians have also died as a result of the war, according to the Cost of War Project, led by researchers Neta C. Crawford and Catherine Lutz of Boston University and Brown University, respectively.
One year after the Afghanistan invasion, Bush made a pitch for a second war, this time in Iraq.
"We know that Iraq and the al-Qaeda terrorist network share a common enemy--the United States of America. We know that Iraq and al-Qaeda have had high-level contacts that go back a decade. Some al-Qaeda leaders who fled Afghanistan went to Iraq," Bush said Oct. 7, 2002, speaking in Ohio.
He went on: "These include one very senior al-Qaeda leader who received medical treatment in Baghdad this year, and who has been associated with planning for chemical and biological attacks. We've learned that Iraq has trained al-Qaeda members in bomb-making and poisons and deadly gases. And we know that after September the 11th, Saddam Hussein's regime gleefully celebrated the terrorist attacks on America."
None of Bush's assertions about Iraq's connection with al-Qaeda have been proven.
On March 20, 2003, a U.S.-led invasion of Iraq marked the beginning of the Iraq war.
Before combat operations ceased in December 2011, 4,475 U.S. soldiers died in Iraq, exceeding the total of deaths on Sept. 11, according to the U.S. Department of Defense.
Numbers of Iraqi civilian casualties vary widely and are the subject of much debate. However, most estimates fall in the range of 105,000 to 114,000 people. Estimates of refugees fleeing Iraq may be as high as 3.2 million.