have not been employed, even in cases when their use would have made strategic or tactical sense. Michael Barnett has taken an evolutionary approach to trace how the norm of political humanitarianism emerged. Martha Finnemore and Kathryn Sikkink distinguish between three types of norms: Regulative norms: they "order and constrain behavior" Constitutive norms: they "create new actors, interests, or categories of action" Evaluative and prescriptive norms: they have an "oughtness" quality to them Finnemore, Sikkink, Jeffrey W. Legro and others have argued that the robustness (or effectiveness) of norms can be measured by factors such as: specificity: norms that are clear and specific are more likely to be effective longevity: norms with a history are more likely to be effective universality: norms that make general claims (rather than localized and particularistic claims) are more likely to be effective prominence: norms that are widely accepted among powerful actors are more likely to be effective Jeffrey Checkel argues that there are two common types of explanations for the efficacy of norms: Rationalism: actors comply with norms due to coercion, cost-benefit calculations, and material incentives Constructivism: actors comply with norms due to social learning and socialization In terms of specific norms, constructivist scholars have shown how the following norms emerged: Humanitarian intervention: Over time, conceptions of who was "human" changed, which led states to increasingly engage in humanitarian interventions in the 20th century. Nuclear taboo: A norm against nuclear weapons developed since 1945. Ban on landmines: Activism by transnational advocacy groups led to a norm prohibiting landmines. Norms of sovereignty. Norms against assassination. Election monitoring. Taboo against the weaponization of water. Anti-whaling norm. Anti-torture norm. Research areas Many constructivists analyse international relations by looking at goals, threats, fears, cultures, identities, and other elements of "social reality" as social facts. In an important edited volume, The Culture of National Security, constructivist scholars—including Elizabeth Kier, Jeffrey Legro, and Peter Katzenstein – challenged many realist assumptions about the dynamics of international politics, particularly in the context of military affairs. Thomas J. Biersteker and Cynthia Weber applied constructivist approaches to understand the evolution of state sovereignty as a central theme in international relations, and works by Rodney Bruce Hall and Daniel Philpott (among others) developed constructivist theories of major transformations in the dynamics of international politics. In international political economy, the application of constructivism has been less frequent. Notable examples of constructivist work in this area include