Answer:
"An attack on one is considered an attack on all."
Step-by-step explanation:
Given that Collective Security is a term that describes a situation whereby individuals, group of people, state or countries comes together to form decision concerning security which ensures and agreed on the basis that the security of one is the interest of all, and therefore commits to a collective response to threats to and breaches to peace.
Hence, in this case, the correct answer is "An attack on one is considered an attack on all."