How did European allies affect the Revolutionary War?
France was the main ally of the Revolutionaries
France joined the fight against Britain(with people such as Rochambeau and Lafayette) in order to get a revenge over its defeat in the Seven Years' War(1756-1763). The period that lasted from the Glorious Revolution in Britain(1688) to Waterloo(1815) is sometimes called the Second One Hundred Years' War since a second century long antagonism between France and Britain took place. This alliance was crucial in determining the outcome of the war and in 1783 the signing of the treaty of Paris made American independence effective.
The French support of the America Revolution was critical to the American victory at Yorktown.
British lose at Saratoga, cost the British an entire army and brought the French in the war on the side of the Americans.
At Yorktown the British lost another entire army and the will to continue the fight against American independence.
The Victory at Yorktown would not have happened without the involvement of the French. The French infantry and artillery worked with the American forces to trap the British army at Yorktown. The French forces helped the Americans to prepare the siege lines that trapped the English. Counter attacks by the British were repulsed as the seasoned and professional French troops fighting with the Americas threw the British back.
Still the trapping of the British army would have accomplished very little without the French fleet. The British armies had been trapped at Boston and rescued by the British fleet. The British had been able to move their forces by sea to New York and South Carolina. The British fleet was sent to rescue the army at Yorktown. The French fleet won a sea battle blocking the rescue by sea. The British commander Cornwallis unable to escape the trap was forced to surrender.
The French allies proved to be the critical element in the British defeat at Yorktown and the British granting America independence.