Under highly repressive regimes, social movement actors may mobilize and engage in collective action when opportunities become available. Favorable opportunities for collective action emerge when repression declines or the state becomes vulnerable to challenge and attack. Repressive regimes that are highly dependent on external powers may have to introduce changes and reforms that are recommended or demanded by their more powerful outside supporters. In the context of weak social bases of support, external pressures to liberalize or open up the polity may generate conditions for large-scale insurgency. Furthermore, reduction of external support may render dependent regimes vulnerable to challenge and attack, which may also be a result of economic and political crises among states generally. In times of national polarization, regimes that have weak bases of support may become vulnerable if they resort to repressive measures to intimidate the opposition. Repressive measures against public figures and well-known challengers may render the state vulnerable by generating a coalition among opposition organizations and major segments of the population.
Given that the Shah's regime was so dependent on outside support, external pressures played an important role in leading the Iranian goffernment to undertake minimal gestures that provided an opportunity for opposition to mobilize. Amnesty International, the International Commission of Jurists, and the UN-affiliated International League for Human Rights began to expose the Iranian government's violations of human rights in the mid-1970s. Amnesty International accused Iran of being one of the world's “worst violators of human rights. ” In the 1976 US presidential campaign, Jimmy Carter singled out Iran as a country where human rights had been violated (Abrahamian 1982: 498–500). Members of the American Congress began to question the wisdom of selling so much weaponry to a regime in which power resided solely in one man.