Collective security is when basically multiple groups/nations form a coalition together and agree to not to attack each other, and to help defend from one another or from another threat.
Countries trade with each other when, on their own, they do not have the resources, or capacity to satisfy their own needs and wants. By developing and exploiting their domestic scarce resources, countries can produce a surplus, and trade this for the resources they need.
leading a military expedition during the Civil War
