What was the watershed battle where american victory insured a huge morale boost and the intervention of france? saratoga trento cowpens yorktown

All four of these battles had a tremendous impact on the flow of the war. Each had a moment in the course of the war as being important. The Battle of Trenton occurred early in the war (1777) as Washington's troops were running low on both supplies and morale. The battle follows the epic crossing of the Delaware River which led to a surprise attack on the German mercenaries, the Hessians. The Battle of Trenton ends in a Hessian surrender giving Washington the Revolutionaries their first real win and ultimately a huge morale boost. The Battle of Cowpens is similar to the Battle of Trenton in it being a small battle with a big morale boost. This battle though takes places toward the end of the war as funds and supplies are running low. The Battle of Cowpens is significant as it turns the tide in the South to the favor of the Revolutionaries. This victory will lead to the Battle of Yorktown which is the site of British surrender. Yorktown will be the final battle of the American Revolution. 
The Battle of Saratoga is widely considered the turning point of the Revolutionary War as the win solidly convinces the French to join the Revolutionaries in the war. France is a much needed ally for the Revolutionaries as they lacked a navy and needed military arms, funding, and training. The French are able to provide this to the Revolutionaries which is considered the tipping point in the war leading to an eventual surrender at Yorktown.