The Battle of Barnet, one of the critical battles in the Wars of the Roses, involved the forces of Edward IV and Richard Neville, the Earl of Warwick. At one time, Edward and Richard had been allies, both of them overthrowing Henry VI (of Lancaster) and putting Edward on the throne. As a reward for his faithfulness to Edward, the Earl of Warwick hoped to earn prestigious positions for his friends at court, but instead Edward gave those positions to supporters of his wife, Queen Elizabeth. This act of disrespect infuriated Richard, and so the earl declared war on Edward. The earl eventually drove Edward into exile and restored Henry VI to his former kingship.
Edward was not done, however. In March 1471, he returned to England with an army of Burgundian mercenaries and marched on London, taking Henry prisoner, and once Henry was in chains, Edward turned his attention on his old friend and ally the Earl of Warwick.
Not far north of London, the two armies met at Barnet in the early morning admist a thick fog. At first, it looked as though Warwick’s men would win the day, but the battle turned, and Edward’s army ended up routing the earl and killing him. After Barnet, Edward won an even greater victory at Tewkesbury, securing his position as king of England.
“Battle of Barnet.” Barnet London Borough. http://www.barnet.gov.uk/index/leisure-culture/libraries/archives/archives-histories/archives-barnethistories/archives-barnet-battleofbarnet.htm (accessed July 13, 2009).
Tompson, Richard S. “Battle of Barnet.” Great Britain: A Reference Guide from the Renaissance to the Present, European Nations. New York: Facts On File, Inc., 2003. Ancient and Medieval History Online. Facts On File, Inc. http://www.fofweb.com/activelink2.asp?
ItemID=WE49&iPin=GB0091&SingleRecord=True (accessed July 13, 2009).
Confrontation at Coventry through the Battle of Barnet, written in Middle-English (primary source)
http://en.wikipedia.org/wiki/Battle_of_Barnet — the Wikipedia entry has some really good information and lots of references and additional sources