Dummer's War (1722–1725) (also known as Father Rale's War, the Three Years War, the Wabanaki-New England War, or the Fourth Anglo-Abenaki War) was a series of battles between the New England Colonies and the Wabanaki Confederacy (specifically the Mi'kmaq, Maliseet, Penobscot, and Abenaki), who were allied with New France. The eastern theater of the war was located primarily along the border between New England and Acadia in Maine, as well as in Nova Scotia; the western theater was located in northern Massachusetts and Vermont in the frontier areas between Canada (New France) and New England.

The root cause of the conflict on the Maine frontier concerned the border between Acadia and New England, which New France defined as the Kennebec River in southern Maine. Mainland Nova Scotia came under British control after the Siege of Port Royal in 1710 and the Treaty of Utrecht in 1713 (not including Cape Breton Island), but present-day New Brunswick and Maine remained contested between New England and New France. New France established Catholic missions among the four largest Native villages in the region: one on the Kennebec River (Norridgewock), one farther north on the Penobscot River (Penobscot Indian Island Reservation), one on the Saint John River (Meductic Indian Village / Fort Meductic), and one at Shubenacadie, Nova Scotia (Saint Anne's Mission). Similarly, New France established three forts along the border of New Brunswick during Father Le Loutre's War to protect it from a British attack from Nova Scotia.

The Treaty of Utrecht ended Queen Anne's War, but it had been signed in Europe and had not involved any member of the Wabanaki Confederacy. The Abenaki signed the 1713 Treaty of Portsmouth, but none had been consulted about British ownership of Nova Scotia, and the Miꞌkmaq began to make raids against New England fishermen and settlements. The war began on two fronts as a result of the expansion of New England settlements along the coast of Maine and at Canso, Nova Scotia. The New Englanders were led primarily by Massachusetts Lieutenant Governor William Dummer, Nova Scotia Lieutenant Governor John Doucett, and Captain John Lovewell. The Wabanaki Confederacy and other Native tribes were led primarily by Father Sébastien Rale, Chief Gray Lock, and Chief Paugus.

During the war, Father Rale was killed by a force of New England militia at Norridgewock. The Native population retreated from the Kennebec and Penobscot rivers to St. Francis and Becancour, Quebec, and New England took over much of the Maine territory.

Dummer's War is also known as the Fourth Anglo-Abenaki War. The three previous Indian Wars were King Philip's War (or the First Indian War) in 1675, King William's War (or the Second Indian War), and Queen Anne's War (or the Third Indian War) from 1703 to 1711.

Queen Anne's War ended with the Treaty of Utrecht in 1713. The colonial borders of northeastern America were reshaped as a result, but the treaty did not account for Indian claims to the same area. French Acadia was ceded to Great Britain which established the province of Nova Scotia, although its borders were disputed. The area disputed by the European powers consisted of land between the Kennebec River and the Isthmus of Chignecto (encompassing the eastern portion of Maine and all of the Canadian province of New Brunswick). This land was occupied by a number of Algonquian-speaking Indian tribes loosely allied in the Wabanaki Confederacy, which also claimed sovereignty over most of this territory and had occupied portions of the land before the colonists.

Massachusetts Governor Joseph Dudley organized a major peace conference at Portsmouth, New Hampshire. In negotiations there and at Casco Bay, the Wabanaki objected to British assertions that the French had ceded their territory to Britain in eastern Maine and New Brunswick, but they agreed to confirm the boundaries at the Kennebec River and to establish government-run trading posts in their territory. The Treaty of Portsmouth was ratified on July 13, 1713, by eight representatives of the Wabanaki Confederacy, however, which asserted British sovereignty over their territory. Over the next year, other Abenaki tribal leaders also signed the treaty, but no Miꞌkmaq ever signed it or any other treaty until 1726.

Following the peace, New England settlements expanded east of the Kennebec River, and significant numbers of New Englanders began fishing in Nova Scotia waters. They established a permanent fishing settlement at Canso, Nova Scotia, which upset the local Miꞌkmaq, who then began raiding the settlement and attacking the fishermen. In response to Wabanaki hostilities, Nova Scotia Governor Richard Philipps built a fort at Canso, Nova Scotia, in 1720. Massachusetts governors Joseph Dudley and Samuel Shute built forts around the mouth of the Kennebec River: Fort George at Brunswick (1715), Fort Menaskoux at Arrowsic (1717), St. George's Fort at Thomaston (1720), and Fort Richmond (1721) at Richmond. The French built a church in the Abenaki village of Norridgewock in Madison, Maine on the Kennebec River, maintained a mission at Penobscot on the Penobscot River, and built a church in the Maliseet village of Meductic on the Saint John River.