Why is the Battle of Saratoga considered a turning point in the American Revolution?

The Battle of Saratoga
(September-October, 1777) was actually a series of battles that culminated with the
surrender of the British force led by General John Burgoyne. Saratoga did indeed prove
to be the turning point of the American Revolution. In addition to being the
most significant American victory up to that point of the war, eliminating a strong
British force in the northern theatre, Saratoga had a greater effect: Both France and
Spain sided with the Americans as allies, and the French contribution proved to be
an essential element of the colonies' eventual victory over Great
Britain.

After first defeating General Horatio Gates'
American army at the Battle of Freeman's Farm on September 19, 1777, Burgoyne was
defeated at the Battle of Bemis Heights on October 7. Burgoyne was forced to retreat and
his army was surrounded by superior American forces at Saratoga on October 17. Following
the British surrender, France's King Louis XVI formally joined into an alliance with the
Americans, forcing the British to divert troops and resources to other theatres of the
war--particularly Europe and the West Indies.

The battle
would ruin Burgoyne's military career and make a legitimate hero of one American
general--the fearless Daniel Morgan--and temporary heroes of two generals who would
later be disgraced: Gates, who would be given command of the Southern army, only to
lead it to disastrous defeat at the Battle of Camden; and Benedict Arnold, who would
soon become America's most famous turncoat when he later went over to the British
side.