Under the Constitution of the United States, an example of a power reserved to the states is the power to

The power to coin money is a responsibility exclusively assigned to the federal government, as outlined in Article I, Section 8 of the Constitution. This centralizes currency production and regulation to maintain a unified economic system across the nation, preventing states from issuing their own currencies, which could lead to confusion and instability.

Regulating interstate commerce is another power granted to the federal government, allowing it to manage trade and economic activities that cross state lines. This authority is established in the Commerce Clause of the Constitution, ensuring a cohesive economic framework and preventing states from enacting conflicting trade regulations that could disrupt national commerce.

The power to declare war is also reserved for the federal government, specifically Congress, as defined in Article I, Section 8. This limitation is intended to prevent states from engaging in independent military actions that could compromise national security or create conflicts with foreign nations.