The Passamaquoddy Indian Tribe (Passamaquoddy) (plaintiff), located in Maine, had numerous dealings with the State of Maine, but little communication or interaction with the federal government. The Passamaquoddy was never the subject of federal treaty or federal law. In the 1970s, a dispute arose between the Passamaquoddy and the State of Maine, which had taken Passamaquoddy land. The Passamaquoddy claimed that in taking the land, the State of Maine had violated the Nonintercourse Act (Act), 25 U.S.C. § 177, which prohibits the purchase of land from Indian tribes unless the purchase is made by treaty or convention under the United States Constitution. The Passamaquoddy asked the United States, through the Secretary of the Interior (United States) (defendant), to sue the State of Maine on behalf of the Passamaquoddy. The Passamaquoddy claimed that the Act created a fiduciary relationship between the United States and the Passamaquoddy and that the United States had a duty to sue on behalf of the Passamaquoddy for violations of the Act. The United States determined that it had no fiduciary relationship with the Passamaquoddy and refused to bring the action. The district court disagreed. The district court held that the United States did have a fiduciary relationship with the Passamaquoddy, despite the absence of federal treaty and the fact that the Passamaquoddy was not a tribe recognized by the United States. The United States appealed.