The Seneca are a group of indigenous Iroquoian-speaking people native to North America who historically lived south of Lake Ontario. They were the nation located farthest to the west within the Six Nations or Iroquois League (Haudenosaunee) in New York before the American Revolution. In the 21st century, more than 10,000 Seneca live in the United States, which has three federally recognized Seneca tribes. Two are in New York: the Seneca Nation of New York, with two reservations in western New York near Buffalo; and the Tonawanda Band of Seneca Native Americans.

On August 25, 1993, the Seneca filed suit in United States District Court to begin an action to reclaim land allegedly taken from it by New York without having gained required approval of the treaty by the United States Senate. Only the US government constitutionally has power to make treaties with the Native American nations. The lands consisted of Grand Island and several smaller islands in the Niagara River. In November 1993, the Tonawanda Band of Seneca Indians moved to join the claim as a plaintiff; it was granted standing as a plaintiff.  In 1998, the United States intervened in the lawsuits on behalf of the plaintiffs in the claim. This was to allow the claim to proceed against New York; the state had asserted that it was immune from suit under the Eleventh Amendment to the United States Constitution. After extensive negotiations and pre-trial procedures, all parties to the claim moved for judgment as a matter of law.  By decision and order dated June 21, 2002, the trial court held that the Seneca ceded the subject lands to Great Britain in the 1764 treaties of peace after the French and Indian War (Seven Years' War). Thus the disputed lands were no longer owned by the Seneca at the time of the 1794 Treaty of Canandaigua. The court found that the state of New York's "purchase" of the lands from the Seneca in 1815 was intended to avoid conflict with them, but the state already owned it by virtue of Great Britain's defeat in the Revolution and cession of its lands to the United States (and by default to the states in which the colonial lands were located.  The Seneca appealed this decision. The United States Court of Appeals for the Second Circuit affirmed the trial court's decision on September 9, 2004. The Seneca sought review of this decision by the US Supreme Court, which on June 5, 2006, announced that it would decline to hear the case, leaving the lower court rulings in place.

Where are the grand islands?
The lands consisted of Grand Island and several smaller islands in the Niagara River.