Nuclear proliferation is the spread of nuclear weapons production technology and knowledge to nations that do not already have such capabilities. It has been opposed by many nations with and without nuclear weapons, who fear that more countries with nuclear weapons may increase the possibility of nuclear warfare, de-stabilize international or regional relations, or infringe upon the national sovereignty of individual nation-states. Other nations have pursued their own independent weapons development, calling into question the authority of some countries being able to specify who can or cannot have their own defensive nuclear weapons.