Fort William and Mary was a colonial fortification in Britain's worldwide system of defenses, defended by soldiers of the Province of New Hampshire who reported directly to the royal governor. The fort, originally known as "The Castle," was situated on the island of New Castle, New Hampshire, at the mouth of the Piscataqua River estuary. It was renamed Fort William and Mary circa 1692, after the accession of the monarchs William III and Mary II to the British throne. It was captured by Patriot forces, recaptured, and later abandoned by the British in the Revolutionary War. The fort was renamed Fort Constitution in 1808 following rebuilding. The fort was further rebuilt and expanded through 1899 and served actively through World War II.

New Hampshire is a state in the New England region of the Northeastern United States. It borders Massachusetts to the south, Vermont to the west, Maine and the Gulf of Maine to the east, and the Canadian province of Quebec to the north. Of the 50 U.S. states, New Hampshire is the fifth smallest by area and the tenth least populous, with a population of 1,377,529 residents as of the 2020 census. Concord is the state capital and Manchester is the most populous city. New Hampshire's motto, "Live Free or Die", reflects its role in the American Revolutionary War; its nickname, "The Granite State", refers to its extensive granite formations and quarries. It is well known nationwide for holding the first primary in the U.S. presidential election cycle, and for its resulting influence on American electoral politics.