Final answer:
Congress has the ability to declare war because it is outlined in the Constitution, specifically in Section 8 Clause 11. The president, on the other hand, does not have the authority to declare war and must rely on congressional authorizations, United Nations resolutions, or other international agreements for military actions.
Step-by-step explanation:
Congress has the ability to declare war because it is outlined in the Constitution. According to Section 8 Clause 11, only Congress can officially declare or make war. This power was given to Congress as a way to ensure that decisions regarding war are made collectively and not in the hands of one person. The president, on the other hand, does not have the authority to declare war and must rely on congressional authorizations, United Nations resolutions, or other international agreements for military actions.