HISTORY IS WRITTEN BY THE VICTORS.

-Unknown

"History is written by victors" may itself be an example of history written by the losers! While the quote is commonly misattributed to Winston Churchill, it's origins are unknown and it might be inspired by Hermann Göring's quote:We will go down in history either as the world's greatest statesmen or its worst villains.

On a perhaps more serious note, the aftermath of the Fall of Constantinople (1453) is a prime example of history written by the losers. A wave of Greek scholars emigrated to the west after the event that essentially marked the end of the Byzantine Empire, bringing with them extremely biased accounts of Ottoman brutality. The vilification of the Ottomans was the prevalent opinion in the Western world for centuries and served as propaganda material as late as 1832, when the Greek War of Independence ended. Even modern attempts at identifying the historical truth of the era, such as the 2011 "1821" documentary, are met with controversy in Greece.A more recent example would be the American Civil War and the Lost Cause movement, a term borrowed from Edward Pollard's 1866 book The Lost Cause: A New Southern History of the War of the Confederates : Comprising a Full and Authentic Account of the Rise and Progress of the Late Southern Confederacy--the Campaigns, Battles, Incidents, and Adventures of the Most Gigantic Struggle of the World's History.Lastly, a (perhaps controversial) example of history written by the losers is the account of the Vietnam War. Although whether the US lost the war is debatable they certainly didn't win it, still the overwhelming majority of historical documentation for the war comes from the US.Further reading:

Michel Foucault's Society Must Be Defended (Lectures at the Collège de France, 1975-76)

Thomas Carlyle's On Heroes and Hero Worship and the Heroic in History, Social history and People's history articles on Wikipedia, Philosophy of history article on Wikipedia, Truth by consensus article on Wikipedia, Historical revisionism article on Wikipedia, History written by the losers article on The Guardian.