Nuclear peace is a theory of international relations that argues that under some circumstances nuclear weapons can induce stability and decrease the chances of crisis escalation. In particular, nuclear weapons are said to have induced stability during the Cold War, when both the US and the USSR possessed mutual second strike retaliation capability, eliminating the possibility of nuclear victory for either side. Proponents of nuclear peace argue that controlled nuclear proliferation may be beneficial for inducing stability. Critics of nuclear peace argue that nuclear proliferation not only increases the chance of interstate nuclear conflict, but increases the chances of nuclear material falling into the hands of violent non-state groups who are free from the threat of nuclear retaliation.