Which event is an example of the alliance system?

a. one country attacks another because a promise i made to a third country

b. a country conquers many other countries to exploit their resources

c. a country loses control of many of its overseas colonies

d. one country engages in a military arm race with another country

An alliance is an agreement between countries to help each other in conflicts and defend each other.  A. One country attacks another because a promise made to a third country is an example of an alliance.  Two countries made a pact and agree to protect each other.  In this situation, it is likely that the first country made an agreement with the third country and is attacking another country on behalf of the third country.

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