A more thorough explanation:

A defensive treaty is an agreement between two or more nations in which each party agrees to come to the aid of the other if one is attacked by another nation. This type of treaty is made to secure the parties against aggression from other states. It may also aim at maintaining internal peace or neutrality amid conflicts of neighboring powers.

For example, the North Atlantic Treaty Organization (NATO) is a defensive treaty in which member countries agree to defend each other if one is attacked. Another example is the Treaty of Mutual Cooperation and Security between the United States and Japan, which obligates the United States to defend Japan if it is attacked.

Defensive treaties are legal and do not violate international law or natural justice. They are made to ensure the safety and security of the parties involved.