How is collective defense defined in international relations?

Collective defense is defined as an agreement among states to defend each other against aggression, which emphasizes mutual security commitments. This concept is foundational in international relations and highlights the idea that an attack against one member of a collective defense arrangement is viewed as an attack against all members. This principle is most famously embodied in treaties such as NATO (North Atlantic Treaty Organization), where member states have pledged to support one another in the face of external threats.

In contrast, options that do not align with this definition lack the element of mutual military commitment in the face of aggression. Economic support, unilateral defense strategies, and diplomatic collaborations focus on different aspects of international relations rather than the specific commitment to mutual defense. Thus, the correct answer effectively encapsulates the essence of collective defense, which revolves around inter-state agreements aimed at ensuring each member's security through joint defensive measures.