In 1947, the United Nations (UN) approved a Trusteeship agreement creating the Trust Territory of the Pacific Islands (TTPI). Previously under Japanese mandate, more than 2,000 islands were placed under the administration of the United States (US). The TTPI differed substantially from other trust territories: Framed as important to global peace (Japan had used the islands to support its attack on Pearl Harbor), the islands were designated as the sole strategic – rather than regular – trust territory, thus placing it under the supervision of the Security Council instead of the Trusteeship Council. Moreover, the trusteeship agreement authorized the US to establish naval, military, and air bases, and to station and employ armed forces in the territory. Situated in the Cold War and atomic age, the TTPI – due to its remoteness – first became a testing ground for nuclear weapons and then a site for nuclear waste disposal, allowing the violation of indigenous rights, the expropriation of land, and the destruction of delicate ecosystems. The chapter investigates the extent of the nuclear experiments on the TTPI and critically analyzes the administration by the US. Moreover, the chapter reflects upon the seemingly anti-colonial stance of the Americans and illustrates the balancing act that the US had to perform between its own geopolitical-strategic ambitions and the anti-imperial liberation policy that it wanted to represent to the outside world. Through the Trusteeship System, the US accomplished an informal acquisition of territory that did not appear as outright colonization. Ultimately, the US abused the islands exclusively for military purposes but could not deliver on the promise of economic advancement. By ignoring its trusteeship obligations, the US succeeded in perpetuating the dependencies and vulnerabilities that justified UN guardianship in the first place, thus managing to tie the islands to itself through bilateral agreements to this day.