Why Do Alliances Form

Why do alliances form?

A) Powerful countries force weaker countries to join their organizations.
B) The citizens of member states push for closer relations with other similar states.
C) An alliance makes members less likely to attack each other.
D) Two or more states have a common goal of promoting peace and realize that the more states that join the organization,the more likely it is that peace will be achieved.
E) Two or more states have a common security goal and need more military support than one of them has.