Which international alliance is dedicated to the mutual defense of its member nations?

NATO, the North Atlantic Treaty Organization, is all about collective defense. It was formed in 1949 in the aftermath of World War II, primarily to counter the perceived threat from the Soviet Union. The core principle is Article 5, which states that an attack on one member is considered an attack on all. So, if any NATO country is attacked, the others are obligated to come to its defense. This is why it's the correct answer. Now, the Red Cross is a humanitarian organization focused on aid and disaster relief, the United Nations aims to promote international cooperation and peace, and UNICEF works to protect children's rights. While all are important international bodies, none are primarily focused on military defense like NATO. Think of it this way: NATO is the security guard, while the others are focused on helping people in different ways.