The Battles of Saratoga (September 19 and October 7, 1777) marked the climax of the Saratoga campaign, giving a decisive victory to the Americans over the British in the American Revolutionary War. British General John Burgoyne led an invasion army of 7,200 men southward from Canada in the Champlain Valley, hoping to meet a similar British force marching northward from New York City and another British force marching eastward from Lake Ontario; the goal was to take Albany, New York. The southern and western forces never arrived, and Burgoyne was surrounded by American forces in upstate New York 15 miles (24 km) short of his goal. He fought two battles which took place 18 days apart on the same ground 9 miles (14 km) south of Saratoga, New York. He gained a victory in the first battle despite being outnumbered, but lost the second battle after the Americans returned with an even larger force.

Burgoyne found himself trapped by much larger American forces with no relief, so he retreated to Saratoga (now Schuylerville) and surrendered his entire army there on October 17. His surrender, says historian Edmund Morgan, "was a great turning point of the war because it won for Americans the foreign assistance which was the last element needed for victory."Burgoyne's strategy to divide New England from the southern colonies had started well but slowed due to logistical problems. He won a small tactical victory over General Horatio Gates and the Continental Army in the September 19 Battle of Freeman's Farm at the cost of significant casualties. His gains were erased when he again attacked the Americans in the October 7 Battle of Bemis Heights and the Americans captured a portion of the British defenses. Burgoyne was therefore compelled to retreat, and his army was surrounded by the much larger American force at Saratoga, forcing him to surrender on October 17. News of Burgoyne's surrender was instrumental in formally bringing France into the war as an American ally, although it had previously given supplies, ammunition, and guns, notably the de Valliere cannon which played an important role in Saratoga.The battle on September 19 began when Burgoyne moved some of his troops in an attempt to flank the entrenched American position on Bemis Heights. Benedict Arnold anticipated the maneuver and placed significant forces in his way. Burgoyne did gain control of Freeman's Farm, but it came at the cost of significant casualties. Skirmishing continued in the days following the battle, while Burgoyne waited in the hope that reinforcements would arrive from New York City. Patriot militia forces continued to arrive, meanwhile, swelling the size of the American army. Disputes within the American camp led Gates to strip Arnold of his command.

British General Sir Henry Clinton moved up from New York City and attempted to divert American attention by capturing Forts Clinton and Montgomery in the Hudson River highlands on October 6, and Kingston on October 13, but his efforts were too late to help Burgoyne. Burgoyne attacked Bemis Heights again on October 7 after it became apparent that he would not receive relieving aid in time. This battle culminated in heavy fighting marked by Arnold's spirited rallying of the American troops. Burgoyne's forces were thrown back to the positions that they held before the September 19 battle, and the Americans captured a portion of the entrenched British defenses.

The American Revolutionary War (April 19, 1775 – September 3, 1783), also known as the Revolutionary War or American War of Independence, secured a United States of America independent from Great Britain. Fighting began on April 19, 1775, followed by the Declaration of Independence on July 4, 1776. The American Patriots were supported by France and Spain, conflict taking place in North America, the Caribbean, and Atlantic Ocean. It ended on September 3, 1783 when Britain accepted American independence in the Treaty of Paris, while the Treaties of Versailles resolved separate conflicts with France and Spain.Established by Royal charter in the 17th and 18th centuries, the American colonies were largely autonomous in domestic affairs and commercially prosperous, trading with Britain and its Caribbean colonies, as well as other European powers via their Caribbean entrepôts. After British victory in the Seven Years' War in 1763, tensions arose over trade, colonial policy in the Northwest Territory and taxation measures, including the Stamp Act and Townshend Acts. Colonial opposition led to the 1770 Boston Massacre and 1773 Boston Tea Party, with Parliament responding by imposing the so-called Intolerable Acts.

On September 5, 1774, the First Continental Congress drafted a Petition to the King and organized a boycott of British goods. Despite attempts to achieve a peaceful solution, fighting began with the Battle of Lexington on April 19, 1775 and in June Congress authorized George Washington to create a Continental Army. Although the "coercion policy" advocated by the North ministry was opposed by a faction within Parliament, both sides increasingly viewed conflict as inevitable. The Olive Branch Petition sent by Congress to George III in July 1775 was rejected and in August Parliament declared the colonies to be in a state of rebellion.

Following the loss of Boston in March 1776, Sir William Howe, the new British commander-in-chief, launched the New York and New Jersey campaign. He captured New York City in November, before Washington won small but significant victories at Trenton and Princeton, which restored Patriot confidence. In summer 1777, Howe succeeded in taking Philadelphia, but in October a separate force under John Burgoyne was forced to surrender at Saratoga. This victory was crucial in convincing powers like France and Spain an independent United States was a viable entity.

France provided the US informal economic and military support from the beginning of the rebellion, and after Saratoga the two countries signed a commercial agreement and a Treaty of Alliance in February 1778. In return for a guarantee of independence, Congress joined France in its global war with Britain and agreed to defend the French West Indies. Spain also allied with France against Britain in the Treaty of Aranjuez (1779), though it did not formally ally with the Americans. Nevertheless, access to ports in Spanish Louisiana allowed the Patriots to import arms and supplies, while the Spanish Gulf Coast campaign deprived the Royal Navy of key bases in the south.

This undermined the 1778 strategy devised by Howe's replacement, Sir Henry Clinton, which took the war into the Southern United States. Despite some initial success, by September 1781 Cornwallis was besieged by a Franco-American force in Yorktown. After an attempt to resupply the garrison failed, Cornwallis surrendered in October, and although the British wars with France and Spain continued for another two years, this ended fighting in North America. In April 1782, the North ministry was replaced by a new British government which accepted American independence and began negotiating the Treaty of Paris, ratified on September 3, 1783.