Final answer:
The power to declare war is given exclusively to the national government, specifically to Congress, as stated in the Constitution.
Step-by-step explanation:
Within the American system, the power to declare war is an enumerated power granted exclusively to the national government. Specifically, this authority is vested in Congress, as outlined in Article I, Section 8 of the Constitution. The Constitution makes clear that several other powers related to maintaining the security of the nation, such as raising and supporting armies and maintaining a navy, are also the responsibility of the federal government.
In contrast, state governments do not possess the power to declare war, as all powers not expressly given to the national government are known as reserved powers and pertain to matters within the state's own borders, such as intrastate commerce and marriage regulations.