King William's War was the North American theater of the Nine Years' War (1688–1697). It was the first of six colonial wars (see the four French and Indian Wars, Father Rale's War and Father Le Loutre's War) fought between New France and New England along with their respective Native allies before France ceded its remaining mainland territories in North America east of the Mississippi River in 1763. It is also known as the Second Indian War, Father Baudoin's War, Castin's War, the Mournful Decade, or the First Intercolonial War (in French).

For King William's War, neither England nor France thought of weakening its position in Europe to support the war effort in North America. New France and the Wabanaki Confederacy were able to thwart New England expansion into Acadia, whose border New France defined as the Kennebec River, now in southern Maine. According to the terms of the 1697 Peace of Ryswick, which ended the Nine Years' War, the boundaries and outposts of New France, New England, and New York remained substantially unchanged.

The war was largely caused by the fact that the treaties and agreements that were reached at the end of the First Indian War (1675–1678) were not adhered to. In addition, the English were alarmed that the Indians were receiving French or maybe Dutch aid. The Indians preyed on the English and their fears by making it look as though they were with the French. The French were fooled as well, as they thought the Indians were working with the English. Those occurrences, in addition to the fact that the English considered the Indians as their subjects, despite the Indians' unwillingness to submit, eventually led to two conflicts, one of which was King William's War.

The English settlers were more than 154,000 at the beginning of the war and outnumbered the French 12 to 1. However, they were divided into multiple colonies along the Atlantic coast, which were unable to cooperate efficiently, and were engulfed in the Glorious Revolution, which created tension among the colonists. In addition, the English lacked military leadership and had a difficult relationship with their native Iroquois allies.

New France was divided into three entities: Acadia on the Atlantic coast; Canada, along the Saint Lawrence River and up to the Great Lakes; and Louisiana, from the Great Lakes to the Gulf of Mexico, along the Mississippi River. The French population amounted to 14,000 in 1689. Although the French were vastly outnumbered, they were more politically unified and contained a disproportionate number of adult males with military backgrounds. Realizing their numerical inferiority, they developed good relationships with the indigenous peoples to multiply their forces and made effective use of hit-and-run tactics.

King James II of England, a Catholic, was deposed at the end of 1688 in the Glorious Revolution during which William III and Mary II, who were Protestants, took the throne. William joined the League of Augsburg in its war against France, which had begun in 1688, where James had fled.

There was significant tension between New France and the northern English colonies in North America, where in 1686, James II had reorganized the separate administrations of the colonies into the Dominion of New England. New England and the Iroquois at times fought New France and their Wabanaki allies. The Iroquois dominated the economically-important Great Lakes fur trade at the time and had been in conflict with New France since 1680. At the urging of New England, the Iroquois interrupted the trade between New France and their western tribal allies through military means. In retaliation, New France raided the lands belonging to the Seneca of western New York. In turn, New England supported the Iroquois in their conflict against New France by raiding the township of Lachine.

There were similar tensions on the border between New England and Acadia, whose boundary New France defined as the Kennebec River, now in southern Maine. English settlers from Massachusetts, whose charter included the Maine area, had by this time expanded their settlements into Acadia. To secure New France's claim to Maine, they established Catholic missions among the three largest Indigenous villages in the region: one on the Kennebec River (Norridgewock); one farther north on the Penobscot River (Penobscot) and one on the Saint John River (Medoctec). For their part, in response to King Philip's War, the five Indigenous tribes in the region of Acadia created the Wabanaki Confederacy to form a political and military alliance with New France to stop the English from further expansion.