collectivesecurity

Collective security is a principle in international relations whereby a group of states commits to respond collectively to any act of aggression against one member. The underlying idea is that aggression against one state threatens the security of all, creating a deterrent effect through expected joint action. In a true collective-security system, all members share responsibility for preventing and countering threats, and no single state can easily override the group's collective decision.

Historically, collective security has appeared most prominently in two major efforts. The League of Nations sought to obligate member states to act in concert against aggression, though it struggled with enforcement and with securing broad participation. After World War II, the United Nations established a more formal framework, with the Security Council empowered to authorize collective measures, including sanctions or military intervention, when there is a threat to peace, a breach of peace, or an act of aggression. In practice, the effectiveness of collective security depends on the willingness and ability of states to act in concert, as decisions often require broad consensus and can be blocked by vetoes from permanent Security Council members.

Mechanisms include political condemnation, economic sanctions, peacekeeping operations, and, when authorized, multinational military action. The Gulf War of 1990–1991 is frequently cited as an example of UN-backed collective security, whereas other interventions reflect more limited or contested forms of collective action. Critiques emphasize sovereignty concerns, inconsistent enforcement, and the risk of free-riding, while modern debates extend the concept to new domains such as cyber security and humanitarian protection under the doctrine of responsibility to protect.