When threats to international peace arose in the 19th and early 20th centuries, states were largely left to self-help mechanisms to ensure their own security. If threats were serious enough, collective action by the major powers (e.g., Concert of Europe) might occur, albeit rarely. After the two World Wars, however, there was an explosion in the number and types of international structures to deal with international crises and the situations that portended them. Central to these efforts was the United Nations (UN), whose Charter (Chapters VI and VII) provided for a series of mechanisms by which the international community could manage threats to international peace. Over time, regional organizations (ROs) such as the African Union (AU) and the Organization of American States, among others, carved out similar conflict management roles.