Arizona v. Navajo Nation

When the United States won the Mexican-American War in 1848, it acquired what became the western part of the United States. For two decades, there were battles between the United States and the peoples now known as the Navajo Nation (Navajos) (plaintiff), who occupied a portion of the acquired territory. The conflict resulted in the execution of a peace treaty in 1868 under which the Navajos agreed not to engage in further battle and the United States agreed to establish a large reservation for the Navajos. Under the treaty, the reservation included, among other things, the right to use needed water on the reservation. The reservation was bordered by the Colorado River, the Little Colorado River, and the San Juan River. The Navajos used water from those rivers as well as water sources on the reservation to meet the reservation’s household, agricultural, industrial, and commercial needs. However, as water scarcity increased in the western United States, water access became an increasing concern for the Navajos. The Navajos eventually sued the United States Department of the Interior, Bureau of Indian Affairs, and other government parties (collectively, the government) (defendants) for breach of trust, alleging that the government was failing to fully satisfy its treaty obligations. The Navajos did not claim that the government had interfered with their water usage. Instead, they argued that the treaty imposed an obligation on the government to take affirmative steps to secure sufficient water for the Navajo reservation, such as by assessing the reservation’s water needs, developing a plan to secure water, and potentially building infrastructure to bring water onto the reservation. The government argued that the treaty did not impose such an obligation. The district court held in the government’s favor, but the Ninth Circuit reversed. The government appealed.