From the horror of 9/11 to the invasion of Iraq; the truth about WMD to the rise of an insurgency; the scandal of Abu Ghraib to the strategy of the surge -- for seven years, FRONTLINE has revealed the defining stories of the war on terror in meticulous detail, and the political dramas that played out at the highest levels of power and influence.

Now, on the fifth anniversary of the Iraq invasion, the full saga unfolds in the two-part FRONTLINE special Bush's War. Veteran FRONTLINE producer Michael Kirk draws on one of the richest archives in broadcast journalism -- more than 40 FRONTLINE reports on Iraq and the war on terror. Combined with fresh reporting and new interviews, Bush's War will be the definitive documentary analysis of one of the most challenging periods in the nation's history.

"Parts of this history have been told before," Kirk says. "But no one has laid out the entire narrative to reveal in one epic story the scope and detail of how this war began and how it has been fought, both on the ground and deep inside the government."

In the fall of 2001, even as America was waging a war in Afghanistan, another hidden war was being waged inside the administration. Part 1 of Bush's War tells the story of this behind-the-scenes battle over whether Iraq would be the next target in the war on terror.

On one side, Secretary of State Colin Powell and Director of Central Intelligence George Tenet squared off against Vice President Dick Cheney and his longtime ally, Secretary of Defense Donald Rumsfeld. The battles were over policy -- whether to attack Iraq; the role of Iraqi exile Ahmad Chalabi; how to treat detainees; whether to seek United Nations resolutions; and the value of intelligence suggesting a connection between Saddam Hussein and the 9/11 attacks -- but the conflict was deeply personal.

"Friendships were dashed," Powell's deputy Richard Armitage tells FRONTLINE. As the war within the administration heated up, Armitage and Powell concluded that they were being shut out of key decisions by Cheney and Rumsfeld. "The battle of ideas, you generally come up with the best solution. When somebody hijacks the system, then, just like a hijacked airplane, very often no good comes of it," Armitage adds.

Others inside the administration believe they understand the motivation behind some of the vice president's actions. "I think the vice president felt he kind of looked death in the eye on 9/11," former White House counterterrorism coordinator Richard Clarke says. "Three thousand Americans died. The building that the vice president used to work in blew up, and people died there. This was a cold slap in the face. This is a different world you're living in now. And the enemy's still out there, and the enemy could come after you. That does cause you to think [about] things differently."

More than anything else, the Iraq war will be the lasting legacy of the Bush presidency. Part 2 of Bush's War examines that war -- beginning with the quick American victory in Iraq, the early mistakes that were made, and then recounting the story of how chaos, looting and violence quickly engulfed the country.

As American forces realized they were unprepared for the looting that followed the invasion, plans for a swift withdrawal of troops were put on hold. With only a few weeks' preparation, American administrator L. Paul Bremer was sent to find a political solution to a rapidly deteriorating situation. Bremer's first moves were to disband the Iraqi military and remove members of Saddam Hussein's party from the government. They were decisions that the original head of reconstruction, Gen. Jay Garner (Ret.), begged Bremer to reconsider at the time. Now they are seen by others as one of the first in a series of missteps that would lead Iraq into a full-blown insurgency.

But Bremer has his defenders: "We believed, Bremer believed, and I think the leadership in Washington believed that it was very important to demonstrate to the Iraqi people that whatever else was going to happen, Saddam and his cronies were not coming back," Walter Slocombe, the national security adviser to Bremer, tells FRONTLINE.

Garner was not the only one on the outside. As senior officials complained about inattention at the top, Gen. Tommy Franks and his deputy, Gen. Michael DeLong -- the generals who had planned the war -- found that decisions were being made without them as well.

"All the recommendations that we were making now in the Phase IV part weren't being taken -- weren't being taken by Bremer or Rumsfeld," DeLong tells FRONTLINE. "That's when Franks said, 'I'm done.' They said, 'Well, you'll be chief of staff of the Army.' He said, 'No, I'm done.'"

What followed is well documented: insurgency, sectarian strife, prisoner abuse and growing casualties. But within the administration, a new battle over strategy was being fought -- this one between a new secretary of state, Condoleezza Rice, and Secretary of Defense Rumsfeld. The clash between America's top diplomat and its chief defense official would go on for more than two years and be settled only after the Republican loss in the 2006 congressional elections. It was then that the president forced Rumsfeld out, ended his strategy of slow withdrawal and ordered a surge of troops. FRONTLINE goes behind closed doors to tell the most recent chapter in this ongoing story, and asks what Bush will leave for a new U.S. president both in Iraq and in the larger war on terror.