In 1981, Palau voted for the world's first nuclear-free constitution. This constitution banned the use, storage and disposal of nuclear, toxic chemical, gas and biological weapons without first being approved by a , or 75 percent, majority in a referendum. This ban delayed Palau's transition to independence, because while negotiating the Compact, the U.S. insisted on the option to operate nuclear propelled vessels and store nuclear weapons within the territory, prompting campaigns for independence and denuclearisation. After several referendums that failed to achieve a ¾ majority, the people of Palau finally approved the Compact in 1994.