Michael Moore's 2004 Iraq War polemic. Won the Palme d'Or; remains the highest-grossing documentary of all time.
From Wikipedia
Fahrenheit 9/11 is a 2004 American documentary film directed, written by, and starring Michael Moore. The subjects of the film are the presidency of George W. Bush, the Iraq War, and the media's coverage of the war. In the film, Moore states that American corporate media were cheerleaders for the 2003 invasion of Iraq, and did not provide an accurate or objective analysis of the rationale for the war and the resulting casualties there.