Answer:
D.Members of an alliance had to defend each other if one went to war.
Arabian sea
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A Roman legion (from Latin legio "military levy, conscription", from legere "to choose") normally indicates the basic ancient Roman army unit recruited specifically from Roman citizens. In reference to the early Roman Kingdom (as opposed to the Roman Republic or Empire), "the legion" means the entire Roman army.
The effect of US government policies during the 1920s is that US national debt declined.