Beginning in 1930, elk in the State of Wyoming (Wyoming) (plaintiff) became infected with brucellosis, a disease that caused miscarriages. In 1985, Wyoming began to vaccinate elk located on state property. Wyoming sought approval from the United States Fish and Wildlife Service (FWS) to vaccinate elk located within Wyoming’s National Elk Refuge (NER). A failure to obtain the FWS’s approval would jeopardize Wyoming’s federal certification as a brucellosis-free cattle industry. The FWS denied Wyoming’s request on the basis that there was inadequate data to determine the vaccine’s safety and effectiveness. For over 10 years, the FWS failed to make a final determination regarding the vaccine’s safety and effectiveness. Wyoming sued the federal government (defendant) in district court, claiming that Wyoming had a sovereign right to manage elk within the NER. A savings clause within the National Wildlife Refuge System Improvement Act (Act), 16 U.S.C. §§ 668dd-ee, stated that the Act should not be construed to limit state authority to manage wildlife within the national wildlife-refuge system. Wyoming also claimed that the FWS’s failure to allow elk vaccinations in the NER violated the Administrative Procedure Act (APA), 5 U.S.C. §§ 701-06. The district court dismissed Wyoming’s complaint, finding that the Act gave the FWS unlimited discretion to manage wildlife in the NER. Wyoming appealed.